Markdown.Editor.js

// needs Markdown.Converter.js at the moment

(function () {

    var util = {},
        position = {},
        ui = {},
        doc = window.document,
        re = window.RegExp,
        nav = window.navigator,
        SETTINGS = { lineLength: 72 },

    // Used to work around some browser bugs where we can't use feature testing.
        uaSniffed = {
            isIE: /msie/.test(nav.userAgent.toLowerCase()),
            isIE_5or6: /msie 6/.test(nav.userAgent.toLowerCase()) || /msie 5/.test(nav.userAgent.toLowerCase()),
            isOpera: /opera/.test(nav.userAgent.toLowerCase())
        };

    var defaultsStrings = {
        bold: "Strong <strong> Ctrl+B",
        boldexample: "strong text",

        italic: "Emphasis <em> Ctrl+I",
        italicexample: "emphasized text",

        link: "Hyperlink <a> Ctrl+L",
        linkdescription: "enter link description here",
        linkdialog: "<p><b>Insert Hyperlink</b></p><p>http://example.com/ \"optional title\"</p>",

        quote: "Blockquote <blockquote> Ctrl+Q",
        quoteexample: "Blockquote",

        code: "Code Sample <pre><code> Ctrl+K",
        codeexample: "enter code here",

        image: "Image <img> Ctrl+G",
        imagedescription: "enter image description here",
        imagedialog: "<p><b>Insert Image</b></p><p>http://example.com/images/diagram.jpg \"optional title\"</p>",

        olist: "Numbered List <ol> Ctrl+O",
        ulist: "Bulleted List <ul> Ctrl+U",
        litem: "List item",

        heading: "Heading <h1>/<h2> Ctrl+H",
        headingexample: "Heading",

        hr: "Horizontal Rule <hr> Ctrl+R",

        undo: "Undo - Ctrl+Z",
        redo: "Redo - Ctrl+Y",
        redomac: "Redo - Ctrl+Shift+Z",

        help: "Markdown Editing Help",

        ok: "OK",
        cancel: "Cancel"
    };


    // -------------------------------------------------------------------
    //  YOUR CHANGES GO HERE
    //
    // I've tried to localize the things you are likely to change to
    // this area.
    // -------------------------------------------------------------------

    // The default text that appears in the dialog input box when entering
    // links.
    var imageDefaultText = "http://";
    var linkDefaultText = "http://";

    // -------------------------------------------------------------------
    //  END OF YOUR CHANGES
    // -------------------------------------------------------------------

    // options, if given, can have the following properties:
    //   options.helpButton = { handler: yourEventHandler }
    //   options.strings = { italicexample: "slanted text" }
    //   options.wrapImageInLink = true
    //   options.convertImagesToLinks = true
    // `yourEventHandler` is the click handler for the help button.
    // If `options.helpButton` isn't given, not help button is created.
    // `options.strings` can have any or all of the same properties as
    // `defaultStrings` above, so you can just override some string displayed
    // to the user on a case-by-case basis, or translate all strings to
    // a different language.
    //
    // For backwards compatibility reasons, the `options` argument can also
    // be just the `helpButton` object, and `strings.help` can also be set via
    // `helpButton.title`. This should be considered legacy.
    //
    // The constructed editor object has the methods:
    // - getConverter() returns the markdown converter object that was passed to the constructor
    // - run() actually starts the editor; should be called after all necessary plugins are registered. Calling this more than once is a no-op.
    // - refreshPreview() forces the preview to be updated. This method is only available after run() was called.
    Markdown.Editor = function (markdownConverter, idPostfix, options) {
        
        options = options || {};

        if (typeof options.handler === "function") { //backwards compatible behavior
            options = { helpButton: options };
        }
        options.strings = options.strings || {};
        if (options.helpButton) {
            options.strings.help = options.strings.help || options.helpButton.title;
        }
        var getString = function (identifier) { return options.strings[identifier] || defaultsStrings[identifier]; }
        
        idPostfix = idPostfix || "";

        this.getPostfix = function () { return idPostfix; }

        var hooks = this.hooks = new Markdown.HookCollection();
        hooks.addNoop("onPreviewRefresh");       // called with no arguments after the preview has been refreshed
        hooks.addNoop("postBlockquoteCreation"); // called with the user's selection *after* the blockquote was created; should return the actual to-be-inserted text
        hooks.addFalse("insertImageDialog");     /* called with one parameter: a callback to be called with the URL of the image. If the application creates
                                                  * its own image insertion dialog, this hook should return true, and the callback should be called with the chosen
                                                  * image url (or null if the user cancelled). If this hook returns false, the default dialog will be used.
                                                  */
        hooks.addNoop("imageConvertedToLink");  // called with no arguments if an image was converted 
        hooks.addFalse("insertLinkDialog");     /* called with one parameter: a callback to be called with the URL.
                                                 * works identical to insertImageDialog (see above)
                                                 */

        this.getConverter = function () { return markdownConverter; }

        var that = this,
            panels;

        this.run = function () {
            if (panels)
                return; // already initialized

            panels = new PanelCollection(idPostfix);
            var commandManager = new CommandManager(hooks, getString, markdownConverter, options.wrapImageInLink, options.convertImagesToLinks);
            var previewManager = new PreviewManager(markdownConverter, panels, function () { hooks.onPreviewRefresh(); });
            var undoManager, uiManager;

            if (!/\?noundo/.test(doc.location.href)) {
                undoManager = new UndoManager(function () {
                    previewManager.refresh();
                    if (uiManager) // not available on the first call
                        uiManager.setUndoRedoButtonStates();
                }, panels);
                this.textOperation = function (f) {
                    undoManager.setCommandMode();
                    f();
                    that.refreshPreview();
                }
            }

            uiManager = new UIManager(idPostfix, panels, undoManager, previewManager, commandManager, options.helpButton, getString);
            uiManager.setUndoRedoButtonStates();

            var forceRefresh = that.refreshPreview = function () { previewManager.refresh(true); };

            forceRefresh();
        };

    }

    // before: contains all the text in the input box BEFORE the selection.
    // after: contains all the text in the input box AFTER the selection.
    function Chunks() { }

    // startRegex: a regular expression to find the start tag
    // endRegex: a regular expresssion to find the end tag
    Chunks.prototype.findTags = function (startRegex, endRegex) {

        var chunkObj = this;
        var regex;

        if (startRegex) {

            regex = util.extendRegExp(startRegex, "", "$");

            this.before = this.before.replace(regex,
                function (match) {
                    chunkObj.startTag = chunkObj.startTag + match;
                    return "";
                });

            regex = util.extendRegExp(startRegex, "^", "");

            this.selection = this.selection.replace(regex,
                function (match) {
                    chunkObj.startTag = chunkObj.startTag + match;
                    return "";
                });
        }

        if (endRegex) {

            regex = util.extendRegExp(endRegex, "", "$");

            this.selection = this.selection.replace(regex,
                function (match) {
                    chunkObj.endTag = match + chunkObj.endTag;
                    return "";
                });

            regex = util.extendRegExp(endRegex, "^", "");

            this.after = this.after.replace(regex,
                function (match) {
                    chunkObj.endTag = match + chunkObj.endTag;
                    return "";
                });
        }
    };

    // If remove is false, the whitespace is transferred
    // to the before/after regions.
    //
    // If remove is true, the whitespace disappears.
    Chunks.prototype.trimWhitespace = function (remove) {
        var beforeReplacer, afterReplacer, that = this;
        if (remove) {
            beforeReplacer = afterReplacer = "";
        } else {
            beforeReplacer = function (s) { that.before += s; return ""; }
            afterReplacer = function (s) { that.after = s + that.after; return ""; }
        }

        this.selection = this.selection.replace(/^(\s*)/, beforeReplacer).replace(/(\s*)$/, afterReplacer);
    };


    Chunks.prototype.skipLines = function (nLinesBefore, nLinesAfter, findExtraNewlines) {

        if (nLinesBefore === undefined) {
            nLinesBefore = 1;
        }

        if (nLinesAfter === undefined) {
            nLinesAfter = 1;
        }

        nLinesBefore++;
        nLinesAfter++;

        var regexText;
        var replacementText;

        // chrome bug ... documented at: http://meta.stackexchange.com/questions/63307/blockquote-glitch-in-editor-in-chrome-6-and-7/65985#65985
        if (navigator.userAgent.match(/Chrome/)) {
            "X".match(/()./);
        }

        this.selection = this.selection.replace(/(^\n*)/, "");

        this.startTag = this.startTag + re.$1;

        this.selection = this.selection.replace(/(\n*$)/, "");
        this.endTag = this.endTag + re.$1;
        this.startTag = this.startTag.replace(/(^\n*)/, "");
        this.before = this.before + re.$1;
        this.endTag = this.endTag.replace(/(\n*$)/, "");
        this.after = this.after + re.$1;

        if (this.before) {

            regexText = replacementText = "";

            while (nLinesBefore--) {
                regexText += "\\n?";
                replacementText += "\n";
            }

            if (findExtraNewlines) {
                regexText = "\\n*";
            }
            this.before = this.before.replace(new re(regexText + "$", ""), replacementText);
        }

        if (this.after) {

            regexText = replacementText = "";

            while (nLinesAfter--) {
                regexText += "\\n?";
                replacementText += "\n";
            }
            if (findExtraNewlines) {
                regexText = "\\n*";
            }

            this.after = this.after.replace(new re(regexText, ""), replacementText);
        }
    };

    // end of Chunks

    // A collection of the important regions on the page.
    // Cached so we don't have to keep traversing the DOM.
    // Also holds ieCachedRange and ieCachedScrollTop, where necessary; working around
    // this issue:
    // Internet explorer has problems with CSS sprite buttons that use HTML
    // lists.  When you click on the background image "button", IE will
    // select the non-existent link text and discard the selection in the
    // textarea.  The solution to this is to cache the textarea selection
    // on the button's mousedown event and set a flag.  In the part of the
    // code where we need to grab the selection, we check for the flag
    // and, if it's set, use the cached area instead of querying the
    // textarea.
    //
    // This ONLY affects Internet Explorer (tested on versions 6, 7
    // and 8) and ONLY on button clicks.  Keyboard shortcuts work
    // normally since the focus never leaves the textarea.
    function PanelCollection(postfix) {
        this.buttonBar = doc.getElementById("wmd-button-bar" + postfix);
        this.preview = doc.getElementById("wmd-preview" + postfix);
        this.input = doc.getElementById("wmd-input" + postfix);
    };

    // Returns true if the DOM element is visible, false if it's hidden.
    // Checks if display is anything other than none.
    util.isVisible = function (elem) {

        if (window.getComputedStyle) {
            // Most browsers
            return window.getComputedStyle(elem, null).getPropertyValue("display") !== "none";
        }
        else if (elem.currentStyle) {
            // IE
            return elem.currentStyle["display"] !== "none";
        }
    };


    // Adds a listener callback to a DOM element which is fired on a specified
    // event.
    util.addEvent = function (elem, event, listener) {
        if (elem.attachEvent) {
            // IE only.  The "on" is mandatory.
            elem.attachEvent("on" + event, listener);
        }
        else {
            // Other browsers.
            elem.addEventListener(event, listener, false);
        }
    };


    // Removes a listener callback from a DOM element which is fired on a specified
    // event.
    util.removeEvent = function (elem, event, listener) {
        if (elem.detachEvent) {
            // IE only.  The "on" is mandatory.
            elem.detachEvent("on" + event, listener);
        }
        else {
            // Other browsers.
            elem.removeEventListener(event, listener, false);
        }
    };

    // Converts \r\n and \r to \n.
    util.fixEolChars = function (text) {
        text = text.replace(/\r\n/g, "\n");
        text = text.replace(/\r/g, "\n");
        return text;
    };

    // Extends a regular expression.  Returns a new RegExp
    // using pre + regex + post as the expression.
    // Used in a few functions where we have a base
    // expression and we want to pre- or append some
    // conditions to it (e.g. adding "$" to the end).
    // The flags are unchanged.
    //
    // regex is a RegExp, pre and post are strings.
    util.extendRegExp = function (regex, pre, post) {

        if (pre === null || pre === undefined) {
            pre = "";
        }
        if (post === null || post === undefined) {
            post = "";
        }

        var pattern = regex.toString();
        var flags;

        // Replace the flags with empty space and store them.
        pattern = pattern.replace(/\/([gim]*)$/, function (wholeMatch, flagsPart) {
            flags = flagsPart;
            return "";
        });

        // Remove the slash delimiters on the regular expression.
        pattern = pattern.replace(/(^\/|\/$)/g, "");
        pattern = pre + pattern + post;

        return new re(pattern, flags);
    }

    // UNFINISHED
    // The assignment in the while loop makes jslint cranky.
    // I'll change it to a better loop later.
    position.getTop = function (elem, isInner) {
        var result = elem.offsetTop;
        if (!isInner) {
            while (elem = elem.offsetParent) {
                result += elem.offsetTop;
            }
        }
        return result;
    };

    position.getHeight = function (elem) {
        return elem.offsetHeight || elem.scrollHeight;
    };

    position.getWidth = function (elem) {
        return elem.offsetWidth || elem.scrollWidth;
    };

    position.getPageSize = function () {

        var scrollWidth, scrollHeight;
        var innerWidth, innerHeight;

        // It's not very clear which blocks work with which browsers.
        if (self.innerHeight && self.scrollMaxY) {
            scrollWidth = doc.body.scrollWidth;
            scrollHeight = self.innerHeight + self.scrollMaxY;
        }
        else if (doc.body.scrollHeight > doc.body.offsetHeight) {
            scrollWidth = doc.body.scrollWidth;
            scrollHeight = doc.body.scrollHeight;
        }
        else {
            scrollWidth = doc.body.offsetWidth;
            scrollHeight = doc.body.offsetHeight;
        }

        if (self.innerHeight) {
            // Non-IE browser
            innerWidth = self.innerWidth;
            innerHeight = self.innerHeight;
        }
        else if (doc.documentElement && doc.documentElement.clientHeight) {
            // Some versions of IE (IE 6 w/ a DOCTYPE declaration)
            innerWidth = doc.documentElement.clientWidth;
            innerHeight = doc.documentElement.clientHeight;
        }
        else if (doc.body) {
            // Other versions of IE
            innerWidth = doc.body.clientWidth;
            innerHeight = doc.body.clientHeight;
        }

        var maxWidth = Math.max(scrollWidth, innerWidth);
        var maxHeight = Math.max(scrollHeight, innerHeight);
        return [maxWidth, maxHeight, innerWidth, innerHeight];
    };

    // Handles pushing and popping TextareaStates for undo/redo commands.
    // I should rename the stack variables to list.
    function UndoManager(callback, panels) {

        var undoObj = this;
        var undoStack = []; // A stack of undo states
        var stackPtr = 0; // The index of the current state
        var mode = "none";
        var lastState; // The last state
        var timer; // The setTimeout handle for cancelling the timer
        var inputStateObj;

        // Set the mode for later logic steps.
        var setMode = function (newMode, noSave) {
            if (mode != newMode) {
                mode = newMode;
                if (!noSave) {
                    saveState();
                }
            }

            if (!uaSniffed.isIE || mode != "moving") {
                timer = setTimeout(refreshState, 1);
            }
            else {
                inputStateObj = null;
            }
        };

        var refreshState = function (isInitialState) {
            inputStateObj = new TextareaState(panels, isInitialState);
            timer = undefined;
        };

        this.setCommandMode = function () {
            mode = "command";
            saveState();
            timer = setTimeout(refreshState, 0);
        };

        this.canUndo = function () {
            return stackPtr > 1;
        };

        this.canRedo = function () {
            if (undoStack[stackPtr + 1]) {
                return true;
            }
            return false;
        };

        // Removes the last state and restores it.
        this.undo = function () {

            if (undoObj.canUndo()) {
                if (lastState) {
                    // What about setting state -1 to null or checking for undefined?
                    lastState.restore();
                    lastState = null;
                }
                else {
                    undoStack[stackPtr] = new TextareaState(panels);
                    undoStack[--stackPtr].restore();

                    if (callback) {
                        callback();
                    }
                }
            }

            mode = "none";
            panels.input.focus();
            refreshState();
        };

        // Redo an action.
        this.redo = function () {

            if (undoObj.canRedo()) {

                undoStack[++stackPtr].restore();

                if (callback) {
                    callback();
                }
            }

            mode = "none";
            panels.input.focus();
            refreshState();
        };

        // Push the input area state to the stack.
        var saveState = function () {
            var currState = inputStateObj || new TextareaState(panels);

            if (!currState) {
                return false;
            }
            if (mode == "moving") {
                if (!lastState) {
                    lastState = currState;
                }
                return;
            }
            if (lastState) {
                if (undoStack[stackPtr - 1].text != lastState.text) {
                    undoStack[stackPtr++] = lastState;
                }
                lastState = null;
            }
            undoStack[stackPtr++] = currState;
            undoStack[stackPtr + 1] = null;
            if (callback) {
                callback();
            }
        };

        var handleCtrlYZ = function (event) {

            var handled = false;

            if ((event.ctrlKey || event.metaKey) && !event.altKey) {

                // IE and Opera do not support charCode.
                var keyCode = event.charCode || event.keyCode;
                var keyCodeChar = String.fromCharCode(keyCode);

                switch (keyCodeChar.toLowerCase()) {

                    case "y":
                        undoObj.redo();
                        handled = true;
                        break;

                    case "z":
                        if (!event.shiftKey) {
                            undoObj.undo();
                        }
                        else {
                            undoObj.redo();
                        }
                        handled = true;
                        break;
                }
            }

            if (handled) {
                if (event.preventDefault) {
                    event.preventDefault();
                }
                if (window.event) {
                    window.event.returnValue = false;
                }
                return;
            }
        };

        // Set the mode depending on what is going on in the input area.
        var handleModeChange = function (event) {

            if (!event.ctrlKey && !event.metaKey) {

                var keyCode = event.keyCode;

                if ((keyCode >= 33 && keyCode <= 40) || (keyCode >= 63232 && keyCode <= 63235)) {
                    // 33 - 40: page up/dn and arrow keys
                    // 63232 - 63235: page up/dn and arrow keys on safari
                    setMode("moving");
                }
                else if (keyCode == 8 || keyCode == 46 || keyCode == 127) {
                    // 8: backspace
                    // 46: delete
                    // 127: delete
                    setMode("deleting");
                }
                else if (keyCode == 13) {
                    // 13: Enter
                    setMode("newlines");
                }
                else if (keyCode == 27) {
                    // 27: escape
                    setMode("escape");
                }
                else if ((keyCode < 16 || keyCode > 20) && keyCode != 91) {
                    // 16-20 are shift, etc.
                    // 91: left window key
                    // I think this might be a little messed up since there are
                    // a lot of nonprinting keys above 20.
                    setMode("typing");
                }
            }
        };

        var setEventHandlers = function () {
            util.addEvent(panels.input, "keypress", function (event) {
                // keyCode 89: y
                // keyCode 90: z
                if ((event.ctrlKey || event.metaKey) && !event.altKey && (event.keyCode == 89 || event.keyCode == 90)) {
                    event.preventDefault();
                }
            });

            var handlePaste = function () {
                if (uaSniffed.isIE || (inputStateObj && inputStateObj.text != panels.input.value)) {
                    if (timer == undefined) {
                        mode = "paste";
                        saveState();
                        refreshState();
                    }
                }
            };

            util.addEvent(panels.input, "keydown", handleCtrlYZ);
            util.addEvent(panels.input, "keydown", handleModeChange);
            util.addEvent(panels.input, "mousedown", function () {
                setMode("moving");
            });

            panels.input.onpaste = handlePaste;
            panels.input.ondrop = handlePaste;
        };

        var init = function () {
            setEventHandlers();
            refreshState(true);
            saveState();
        };

        init();
    }

    // end of UndoManager

    // The input textarea state/contents.
    // This is used to implement undo/redo by the undo manager.
    function TextareaState(panels, isInitialState) {

        // Aliases
        var stateObj = this;
        var inputArea = panels.input;
        this.init = function () {
            if (!util.isVisible(inputArea)) {
                return;
            }
            if (!isInitialState && doc.activeElement && doc.activeElement !== inputArea) { // this happens when tabbing out of the input box
                return;
            }

            this.setInputAreaSelectionStartEnd();
            this.scrollTop = inputArea.scrollTop;
            if (!this.text && inputArea.selectionStart || inputArea.selectionStart === 0) {
                this.text = inputArea.value;
            }

        }

        // Sets the selected text in the input box after we've performed an
        // operation.
        this.setInputAreaSelection = function () {

            if (!util.isVisible(inputArea)) {
                return;
            }

            if (inputArea.selectionStart !== undefined && !uaSniffed.isOpera) {

                inputArea.focus();
                inputArea.selectionStart = stateObj.start;
                inputArea.selectionEnd = stateObj.end;
                inputArea.scrollTop = stateObj.scrollTop;
            }
            else if (doc.selection) {

                if (doc.activeElement && doc.activeElement !== inputArea) {
                    return;
                }

                inputArea.focus();
                var range = inputArea.createTextRange();
                range.moveStart("character", -inputArea.value.length);
                range.moveEnd("character", -inputArea.value.length);
                range.moveEnd("character", stateObj.end);
                range.moveStart("character", stateObj.start);
                range.select();
            }
        };

        this.setInputAreaSelectionStartEnd = function () {

            if (!panels.ieCachedRange && (inputArea.selectionStart || inputArea.selectionStart === 0)) {

                stateObj.start = inputArea.selectionStart;
                stateObj.end = inputArea.selectionEnd;
            }
            else if (doc.selection) {

                stateObj.text = util.fixEolChars(inputArea.value);

                // IE loses the selection in the textarea when buttons are
                // clicked.  On IE we cache the selection. Here, if something is cached,
                // we take it.
                var range = panels.ieCachedRange || doc.selection.createRange();

                var fixedRange = util.fixEolChars(range.text);
                var marker = "\x07";
                var markedRange = marker + fixedRange + marker;
                range.text = markedRange;
                var inputText = util.fixEolChars(inputArea.value);

                range.moveStart("character", -markedRange.length);
                range.text = fixedRange;

                stateObj.start = inputText.indexOf(marker);
                stateObj.end = inputText.lastIndexOf(marker) - marker.length;

                var len = stateObj.text.length - util.fixEolChars(inputArea.value).length;

                if (len) {
                    range.moveStart("character", -fixedRange.length);
                    while (len--) {
                        fixedRange += "\n";
                        stateObj.end += 1;
                    }
                    range.text = fixedRange;
                }

                if (panels.ieCachedRange)
                    stateObj.scrollTop = panels.ieCachedScrollTop; // this is set alongside with ieCachedRange

                panels.ieCachedRange = null;

                this.setInputAreaSelection();
            }
        };

        // Restore this state into the input area.
        this.restore = function () {

            if (stateObj.text != undefined && stateObj.text != inputArea.value) {
                inputArea.value = stateObj.text;
            }
            this.setInputAreaSelection();
            inputArea.scrollTop = stateObj.scrollTop;
        };

        // Gets a collection of HTML chunks from the inptut textarea.
        this.getChunks = function () {

            var chunk = new Chunks();
            chunk.before = util.fixEolChars(stateObj.text.substring(0, stateObj.start));
            chunk.startTag = "";
            chunk.selection = util.fixEolChars(stateObj.text.substring(stateObj.start, stateObj.end));
            chunk.endTag = "";
            chunk.after = util.fixEolChars(stateObj.text.substring(stateObj.end));
            chunk.scrollTop = stateObj.scrollTop;

            return chunk;
        };

        // Sets the TextareaState properties given a chunk of markdown.
        this.setChunks = function (chunk) {

            chunk.before = chunk.before + chunk.startTag;
            chunk.after = chunk.endTag + chunk.after;

            this.start = chunk.before.length;
            this.end = chunk.before.length + chunk.selection.length;
            this.text = chunk.before + chunk.selection + chunk.after;
            this.scrollTop = chunk.scrollTop;
        };
        this.init();
    };

    function PreviewManager(converter, panels, previewRefreshCallback) {

        var managerObj = this;
        var timeout;
        var elapsedTime;
        var oldInputText;
        var maxDelay = 3000;
        var startType = "delayed"; // The other legal value is "manual"

        // Adds event listeners to elements
        var setupEvents = function (inputElem, listener) {

            util.addEvent(inputElem, "input", listener);
            inputElem.onpaste = listener;
            inputElem.ondrop = listener;

            util.addEvent(inputElem, "keypress", listener);
            util.addEvent(inputElem, "keydown", listener);
        };

        var getDocScrollTop = function () {

            var result = 0;

            if (window.innerHeight) {
                result = window.pageYOffset;
            }
            else
                if (doc.documentElement && doc.documentElement.scrollTop) {
                    result = doc.documentElement.scrollTop;
                }
                else
                    if (doc.body) {
                        result = doc.body.scrollTop;
                    }

            return result;
        };

        var makePreviewHtml = function () {

            // If there is no registered preview panel
            // there is nothing to do.
            if (!panels.preview)
                return;


            var text = panels.input.value;
            if (text && text == oldInputText) {
                return; // Input text hasn't changed.
            }
            else {
                oldInputText = text;
            }

            var prevTime = new Date().getTime();

            text = converter.makeHtml(text);

            // Calculate the processing time of the HTML creation.
            // It's used as the delay time in the event listener.
            var currTime = new Date().getTime();
            elapsedTime = currTime - prevTime;

            pushPreviewHtml(text);
        };

        // setTimeout is already used.  Used as an event listener.
        var applyTimeout = function () {

            if (timeout) {
                clearTimeout(timeout);
                timeout = undefined;
            }

            if (startType !== "manual") {

                var delay = 0;

                if (startType === "delayed") {
                    delay = elapsedTime;
                }

                if (delay > maxDelay) {
                    delay = maxDelay;
                }
                timeout = setTimeout(makePreviewHtml, delay);
            }
        };

        var getScaleFactor = function (panel) {
            if (panel.scrollHeight <= panel.clientHeight) {
                return 1;
            }
            return panel.scrollTop / (panel.scrollHeight - panel.clientHeight);
        };

        var setPanelScrollTops = function () {
            if (panels.preview) {
                panels.preview.scrollTop = (panels.preview.scrollHeight - panels.preview.clientHeight) * getScaleFactor(panels.preview);
            }
        };

        this.refresh = function (requiresRefresh) {

            if (requiresRefresh) {
                oldInputText = "";
                makePreviewHtml();
            }
            else {
                applyTimeout();
            }
        };

        this.processingTime = function () {
            return elapsedTime;
        };

        var isFirstTimeFilled = true;

        // IE doesn't let you use innerHTML if the element is contained somewhere in a table
        // (which is the case for inline editing) -- in that case, detach the element, set the
        // value, and reattach. Yes, that *is* ridiculous.
        var ieSafePreviewSet = function (text) {
            var preview = panels.preview;
            var parent = preview.parentNode;
            var sibling = preview.nextSibling;
            parent.removeChild(preview);
            preview.innerHTML = text;
            if (!sibling)
                parent.appendChild(preview);
            else
                parent.insertBefore(preview, sibling);
        }

        var nonSuckyBrowserPreviewSet = function (text) {
            panels.preview.innerHTML = text;
        }

        var previewSetter;

        var previewSet = function (text) {
            if (previewSetter)
                return previewSetter(text);

            try {
                nonSuckyBrowserPreviewSet(text);
                previewSetter = nonSuckyBrowserPreviewSet;
            } catch (e) {
                previewSetter = ieSafePreviewSet;
                previewSetter(text);
            }
        };

        var pushPreviewHtml = function (text) {

            var emptyTop = position.getTop(panels.input) - getDocScrollTop();

            if (panels.preview) {
                previewSet(text);
                previewRefreshCallback();
            }

            setPanelScrollTops();

            if (isFirstTimeFilled) {
                isFirstTimeFilled = false;
                return;
            }

            var fullTop = position.getTop(panels.input) - getDocScrollTop();

            if (uaSniffed.isIE) {
                setTimeout(function () {
                    window.scrollBy(0, fullTop - emptyTop);
                }, 0);
            }
            else {
                window.scrollBy(0, fullTop - emptyTop);
            }
        };

        var init = function () {

            setupEvents(panels.input, applyTimeout);
            makePreviewHtml();

            if (panels.preview) {
                panels.preview.scrollTop = 0;
            }
        };

        init();
    };

    // Creates the background behind the hyperlink text entry box.
    // And download dialog
    // Most of this has been moved to CSS but the div creation and
    // browser-specific hacks remain here.
    ui.createBackground = function () {

        var background = doc.createElement("div"),
            style = background.style;
        
        background.className = "wmd-prompt-background";
        
        style.position = "absolute";
        style.top = "0";

        style.zIndex = "1000";

        if (uaSniffed.isIE) {
            style.filter = "alpha(opacity=50)";
        }
        else {
            style.opacity = "0.5";
        }

        var pageSize = position.getPageSize();
        style.height = pageSize[1] + "px";

        if (uaSniffed.isIE) {
            style.left = doc.documentElement.scrollLeft;
            style.width = doc.documentElement.clientWidth;
        }
        else {
            style.left = "0";
            style.width = "100%";
        }

        doc.body.appendChild(background);
        return background;
    };

    // This simulates a modal dialog box and asks for the URL when you
    // click the hyperlink or image buttons.
    //
    // text: The html for the input box.
    // defaultInputText: The default value that appears in the input box.
    // ok: The text for the OK button
    // cancel: The text for the Cancel button
    // callback: The function which is executed when the prompt is dismissed, either via OK or Cancel.
    //      It receives a single argument; either the entered text (if OK was chosen) or null (if Cancel
    //      was chosen).
    ui.prompt = function (text, defaultInputText, ok, cancel, callback) {

        // These variables need to be declared at this level since they are used
        // in multiple functions.
        var dialog;         // The dialog box.
        var input;         // The text box where you enter the hyperlink.


        if (defaultInputText === undefined) {
            defaultInputText = "";
        }

        // Used as a keydown event handler. Esc dismisses the prompt.
        // Key code 27 is ESC.
        var checkEscape = function (key) {
            var code = (key.charCode || key.keyCode);
            if (code === 27) {
                if (key.stopPropagation) key.stopPropagation();
                close(true);
                return false;
            }
        };

        // Dismisses the hyperlink input box.
        // isCancel is true if we don't care about the input text.
        // isCancel is false if we are going to keep the text.
        var close = function (isCancel) {
            util.removeEvent(doc.body, "keyup", checkEscape);
            var text = input.value;

            if (isCancel) {
                text = null;
            }
            else {
                // Fixes common pasting errors.
                text = text.replace(/^http:\/\/(https?|ftp):\/\//, '$1://');
                if (!/^(?:https?|ftp):\/\//.test(text))
                    text = 'http://' + text;
            }

            dialog.parentNode.removeChild(dialog);

            callback(text);
            return false;
        };



        // Create the text input box form/window.
        var createDialog = function (ok, cancel) {

            // The main dialog box.
            dialog = doc.createElement("div");
            dialog.className = "wmd-prompt-dialog";
            dialog.style.padding = "10px;";
            dialog.style.position = "fixed";
            dialog.style.width = "400px";
            dialog.style.zIndex = "1001";

            // The dialog text.
            var question = doc.createElement("div");
            question.innerHTML = text;
            question.style.padding = "5px";
            dialog.appendChild(question);

            // The web form container for the text box and buttons.
            var form = doc.createElement("form"),
                style = form.style;
            form.onsubmit = function () { return close(false); };
            style.padding = "0";
            style.margin = "0";
            style.cssFloat = "left";
            style.width = "100%";
            style.textAlign = "center";
            style.position = "relative";
            dialog.appendChild(form);

            // The input text box
            input = doc.createElement("input");
            input.type = "text";
            input.value = defaultInputText;
            style = input.style;
            style.display = "block";
            style.width = "80%";
            style.marginLeft = style.marginRight = "auto";
            form.appendChild(input);

            // The ok button
            var okButton = doc.createElement("input");
            okButton.type = "button";
            okButton.onclick = function () { return close(false); };
            okButton.value = ok;
            style = okButton.style;
            style.margin = "10px";
            style.display = "inline";
            style.width = "7em";


            // The cancel button
            var cancelButton = doc.createElement("input");
            cancelButton.type = "button";
            cancelButton.onclick = function () { return close(true); };
            cancelButton.value = cancel;
            style = cancelButton.style;
            style.margin = "10px";
            style.display = "inline";
            style.width = "7em";

            form.appendChild(okButton);
            form.appendChild(cancelButton);

            util.addEvent(doc.body, "keyup", checkEscape);
            dialog.style.top = "50%";
            dialog.style.left = "50%";
            dialog.style.display = "block";
            if (uaSniffed.isIE_5or6) {
                dialog.style.position = "absolute";
                dialog.style.top = doc.documentElement.scrollTop + 200 + "px";
                dialog.style.left = "50%";
            }
            doc.body.appendChild(dialog);

            // This has to be done AFTER adding the dialog to the form if you
            // want it to be centered.
            dialog.style.marginTop = -(position.getHeight(dialog) / 2) + "px";
            dialog.style.marginLeft = -(position.getWidth(dialog) / 2) + "px";

        };
        // Why is this in a zero-length timeout?
        // Is it working around a browser bug?
        setTimeout(function () {

            createDialog(ok, cancel);

            var defTextLen = defaultInputText.length;
            if (input.selectionStart !== undefined) {
                input.selectionStart = 0;
                input.selectionEnd = defTextLen;
            }
            else if (input.createTextRange) {
                var range = input.createTextRange();
                range.collapse(false);
                range.moveStart("character", -defTextLen);
                range.moveEnd("character", defTextLen);
                range.select();
            }

            input.focus();
        }, 0);
    };

    function UIManager(postfix, panels, undoManager, previewManager, commandManager, helpOptions, getString) {

        var inputBox = panels.input,
            buttons = {}; // buttons.undo, buttons.link, etc. The actual DOM elements.

        makeSpritedButtonRow();

        var keyEvent = "keydown";
        if (uaSniffed.isOpera) {
            keyEvent = "keypress";
        }

        util.addEvent(inputBox, keyEvent, function (key) {

            // Check to see if we have a button key and, if so execute the callback.
            if ((key.ctrlKey || key.metaKey) && !key.altKey && !key.shiftKey) {

                var keyCode = key.charCode || key.keyCode;
                var keyCodeStr = String.fromCharCode(keyCode).toLowerCase();

                switch (keyCodeStr) {
                    case "b":
                        doClick(buttons.bold);
                        break;
                    case "i":
                        doClick(buttons.italic);
                        break;
                    case "l":
                        doClick(buttons.link);
                        break;
                    case "q":
                        doClick(buttons.quote);
                        break;
                    case "k":
                        doClick(buttons.code);
                        break;
                    case "g":
                        doClick(buttons.image);
                        break;
                    case "o":
                        doClick(buttons.olist);
                        break;
                    case "u":
                        doClick(buttons.ulist);
                        break;
                    case "h":
                        doClick(buttons.heading);
                        break;
                    case "r":
                        doClick(buttons.hr);
                        break;
                    case "y":
                        doClick(buttons.redo);
                        break;
                    case "z":
                        if (key.shiftKey) {
                            doClick(buttons.redo);
                        }
                        else {
                            doClick(buttons.undo);
                        }
                        break;
                    default:
                        return;
                }


                if (key.preventDefault) {
                    key.preventDefault();
                }

                if (window.event) {
                    window.event.returnValue = false;
                }
            }
        });

        // Auto-indent on shift-enter
        util.addEvent(inputBox, "keyup", function (key) {
            if (key.shiftKey && !key.ctrlKey && !key.metaKey) {
                var keyCode = key.charCode || key.keyCode;
                // Character 13 is Enter
                if (keyCode === 13) {
                    var fakeButton = {};
                    fakeButton.textOp = bindCommand("doAutoindent");
                    doClick(fakeButton);
                }
            }
        });

        // special handler because IE clears the context of the textbox on ESC
        if (uaSniffed.isIE) {
            util.addEvent(inputBox, "keydown", function (key) {
                var code = key.keyCode;
                if (code === 27) {
                    return false;
                }
            });
        }


        // Perform the button's action.
        function doClick(button) {

            inputBox.focus();

            if (button.textOp) {

                if (undoManager) {
                    undoManager.setCommandMode();
                }

                var state = new TextareaState(panels);

                if (!state) {
                    return;
                }

                var chunks = state.getChunks();

                // Some commands launch a "modal" prompt dialog.  Javascript
                // can't really make a modal dialog box and the WMD code
                // will continue to execute while the dialog is displayed.
                // This prevents the dialog pattern I'm used to and means
                // I can't do something like this:
                //
                // var link = CreateLinkDialog();
                // makeMarkdownLink(link);
                //
                // Instead of this straightforward method of handling a
                // dialog I have to pass any code which would execute
                // after the dialog is dismissed (e.g. link creation)
                // in a function parameter.
                //
                // Yes this is awkward and I think it sucks, but there's
                // no real workaround.  Only the image and link code
                // create dialogs and require the function pointers.
                var fixupInputArea = function () {

                    inputBox.focus();

                    if (chunks) {
                        state.setChunks(chunks);
                    }

                    state.restore();
                    previewManager.refresh();
                };

                var noCleanup = button.textOp(chunks, fixupInputArea);

                if (!noCleanup) {
                    fixupInputArea();
                }

            }

            if (button.execute) {
                button.execute(undoManager);
            }
        };

        function setupButton(button, isEnabled) {

            var normalYShift = "0px";
            var disabledYShift = "-20px";
            var highlightYShift = "-40px";
            var image = button.getElementsByTagName("span")[0];
            if (isEnabled) {
                image.style.backgroundPosition = button.XShift + " " + normalYShift;
                button.onmouseover = function () {
                    image.style.backgroundPosition = this.XShift + " " + highlightYShift;
                };

                button.onmouseout = function () {
                    image.style.backgroundPosition = this.XShift + " " + normalYShift;
                };

                // IE tries to select the background image "button" text (it's
                // implemented in a list item) so we have to cache the selection
                // on mousedown.
                if (uaSniffed.isIE) {
                    button.onmousedown = function () {
                        if (doc.activeElement && doc.activeElement !== panels.input) { // we're not even in the input box, so there's no selection
                            return;
                        }
                        panels.ieCachedRange = document.selection.createRange();
                        panels.ieCachedScrollTop = panels.input.scrollTop;
                    };
                }

                if (!button.isHelp) {
                    button.onclick = function () {
                        if (this.onmouseout) {
                            this.onmouseout();
                        }
                        doClick(this);
                        return false;
                    }
                }
            }
            else {
                image.style.backgroundPosition = button.XShift + " " + disabledYShift;
                button.onmouseover = button.onmouseout = button.onclick = function () { };
            }
        }

        function bindCommand(method) {
            if (typeof method === "string")
                method = commandManager[method];
            return function () { method.apply(commandManager, arguments); }
        }

        function makeSpritedButtonRow() {

            var buttonBar = panels.buttonBar;

            var normalYShift = "0px";
            var disabledYShift = "-20px";
            var highlightYShift = "-40px";

            var buttonRow = document.createElement("ul");
            buttonRow.id = "wmd-button-row" + postfix;
            buttonRow.className = 'wmd-button-row';
            buttonRow = buttonBar.appendChild(buttonRow);
            var xPosition = 0;
            var makeButton = function (id, title, XShift, textOp) {
                var button = document.createElement("li");
                button.className = "wmd-button";
                button.style.left = xPosition + "px";
                xPosition += 25;
                var buttonImage = document.createElement("span");
                button.id = id + postfix;
                button.appendChild(buttonImage);
                button.title = title;
                button.XShift = XShift;
                if (textOp)
                    button.textOp = textOp;
                setupButton(button, true);
                buttonRow.appendChild(button);
                return button;
            };
            var makeSpacer = function (num) {
                var spacer = document.createElement("li");
                spacer.className = "wmd-spacer wmd-spacer" + num;
                spacer.id = "wmd-spacer" + num + postfix;
                buttonRow.appendChild(spacer);
                xPosition += 25;
            }

            buttons.bold = makeButton("wmd-bold-button", getString("bold"), "0px", bindCommand("doBold"));
            buttons.italic = makeButton("wmd-italic-button", getString("italic"), "-20px", bindCommand("doItalic"));
            makeSpacer(1);
            buttons.link = makeButton("wmd-link-button", getString("link"), "-40px", bindCommand(function (chunk, postProcessing) {
                return this.doLinkOrImage(chunk, postProcessing, false);
            }));
            buttons.quote = makeButton("wmd-quote-button", getString("quote"), "-60px", bindCommand("doBlockquote"));
            buttons.code = makeButton("wmd-code-button", getString("code"), "-80px", bindCommand("doCode"));
            buttons.image = makeButton("wmd-image-button", getString("image"), "-100px", bindCommand(function (chunk, postProcessing) {
                return this.doLinkOrImage(chunk, postProcessing, true);
            }));
            makeSpacer(2);
            buttons.olist = makeButton("wmd-olist-button", getString("olist"), "-120px", bindCommand(function (chunk, postProcessing) {
                this.doList(chunk, postProcessing, true);
            }));
            buttons.ulist = makeButton("wmd-ulist-button", getString("ulist"), "-140px", bindCommand(function (chunk, postProcessing) {
                this.doList(chunk, postProcessing, false);
            }));
            buttons.heading = makeButton("wmd-heading-button", getString("heading"), "-160px", bindCommand("doHeading"));
            buttons.hr = makeButton("wmd-hr-button", getString("hr"), "-180px", bindCommand("doHorizontalRule"));
            makeSpacer(3);
            buttons.undo = makeButton("wmd-undo-button", getString("undo"), "-200px", null);
            buttons.undo.execute = function (manager) { if (manager) manager.undo(); };

            var redoTitle = /win/.test(nav.platform.toLowerCase()) ?
                getString("redo") :
                getString("redomac"); // mac and other non-Windows platforms

            buttons.redo = makeButton("wmd-redo-button", redoTitle, "-220px", null);
            buttons.redo.execute = function (manager) { if (manager) manager.redo(); };

            if (helpOptions) {
                var helpButton = document.createElement("li");
                var helpButtonImage = document.createElement("span");
                helpButton.appendChild(helpButtonImage);
                helpButton.className = "wmd-button wmd-help-button";
                helpButton.id = "wmd-help-button" + postfix;
                helpButton.XShift = "-240px";
                helpButton.isHelp = true;
                helpButton.style.right = "0px";
                helpButton.title = getString("help");
                helpButton.onclick = helpOptions.handler;

                setupButton(helpButton, true);
                buttonRow.appendChild(helpButton);
                buttons.help = helpButton;
            }

            setUndoRedoButtonStates();
        }

        function setUndoRedoButtonStates() {
            if (undoManager) {
                setupButton(buttons.undo, undoManager.canUndo());
                setupButton(buttons.redo, undoManager.canRedo());
            }
        };

        this.setUndoRedoButtonStates = setUndoRedoButtonStates;

    }

    function CommandManager(pluginHooks, getString, converter, wrapImageInLink, convertImagesToLinks) {
        this.hooks = pluginHooks;
        this.getString = getString;
        this.converter = converter;
        this.wrapImageInLink = wrapImageInLink;
        this.convertImagesToLinks = convertImagesToLinks;
    }

    var commandProto = CommandManager.prototype;

    // The markdown symbols - 4 spaces = code, > = blockquote, etc.
    commandProto.prefixes = "(?:\\s{4,}|\\s*>|\\s*-\\s+|\\s*\\d+\\.|=|\\+|-|_|\\*|#|\\s*\\[[^\n]]+\\]:)";

    // Remove markdown symbols from the chunk selection.
    commandProto.unwrap = function (chunk) {
        var txt = new re("([^\\n])\\n(?!(\\n|" + this.prefixes + "))", "g");
        chunk.selection = chunk.selection.replace(txt, "$1 $2");
    };

    commandProto.wrap = function (chunk, len) {
        this.unwrap(chunk);
        var regex = new re("(.{1," + len + "})( +|$\\n?)", "gm"),
            that = this;

        chunk.selection = chunk.selection.replace(regex, function (line, marked) {
            if (new re("^" + that.prefixes, "").test(line)) {
                return line;
            }
            return marked + "\n";
        });

        chunk.selection = chunk.selection.replace(/\s+$/, "");
    };

    commandProto.doBold = function (chunk, postProcessing) {
        return this.doBorI(chunk, postProcessing, 2, this.getString("boldexample"));
    };

    commandProto.doItalic = function (chunk, postProcessing) {
        return this.doBorI(chunk, postProcessing, 1, this.getString("italicexample"));
    };

    // chunk: The selected region that will be enclosed with */**
    // nStars: 1 for italics, 2 for bold
    // insertText: If you just click the button without highlighting text, this gets inserted
    commandProto.doBorI = function (chunk, postProcessing, nStars, insertText) {

        // Get rid of whitespace and fixup newlines.
        chunk.trimWhitespace();
        chunk.selection = chunk.selection.replace(/\n{2,}/g, "\n");

        // Look for stars before and after.  Is the chunk already marked up?
        // note that these regex matches cannot fail
        var starsBefore = /(\**$)/.exec(chunk.before)[0];
        var starsAfter = /(^\**)/.exec(chunk.after)[0];

        var prevStars = Math.min(starsBefore.length, starsAfter.length);

        // Remove stars if we have to since the button acts as a toggle.
        if ((prevStars >= nStars) && (prevStars != 2 || nStars != 1)) {
            chunk.before = chunk.before.replace(re("[*]{" + nStars + "}$", ""), "");
            chunk.after = chunk.after.replace(re("^[*]{" + nStars + "}", ""), "");
        }
        else if (!chunk.selection && starsAfter) {
            // It's not really clear why this code is necessary.  It just moves
            // some arbitrary stuff around.
            chunk.after = chunk.after.replace(/^([*_]*)/, "");
            chunk.before = chunk.before.replace(/(\s?)$/, "");
            var whitespace = re.$1;
            chunk.before = chunk.before + starsAfter + whitespace;
        }
        else {

            // In most cases, if you don't have any selected text and click the button
            // you'll get a selected, marked up region with the default text inserted.
            if (!chunk.selection && !starsAfter) {
                chunk.selection = insertText;
            }

            // Add the true markup.
            var markup = nStars <= 1 ? "*" : "**"; // shouldn't the test be = ?
            chunk.before = chunk.before + markup;
            chunk.after = markup + chunk.after;
        }

        return;
    };

    commandProto.stripLinkDefs = function (text, defsToAdd) {

        text = text.replace(/^[ ]{0,3}\[(\d+)\]:[ \t]*\n?[ \t]*<?(\S+?)>?[ \t]*\n?[ \t]*(?:(\n*)["(](.+?)[")][ \t]*)?(?:\n+|$)/gm,
            function (totalMatch, id, link, newlines, title) {
                defsToAdd[id] = totalMatch.replace(/\s*$/, "");
                if (newlines) {
                    // Strip the title and return that separately.
                    defsToAdd[id] = totalMatch.replace(/["(](.+?)[")]$/, "");
                    return newlines + title;
                }
                return "";
            });

        return text;
    };

    commandProto.addLinkDef = function (chunk, linkDef) {

        var refNumber = 0; // The current reference number
        var defsToAdd = {}; //
        // Start with a clean slate by removing all previous link definitions.
        chunk.before = this.stripLinkDefs(chunk.before, defsToAdd);
        chunk.selection = this.stripLinkDefs(chunk.selection, defsToAdd);
        chunk.after = this.stripLinkDefs(chunk.after, defsToAdd);

        var defs = "";
        var regex = /\[(\d+)\]/g;
        
        // The above regex, used to update [foo][13] references after renumbering,
        // is much too liberal; it can catch things that are not actually parsed
        // as references (notably: code). It's impossible to know which matches are
        // real references without performing a markdown conversion, so that's what
        // we do. All matches are replaced with a unique reference number, which is
        // given a unique link. The uniquifier in both cases is the character offset
        // of the match inside the source string. The modified version is then sent
        // through the Markdown renderer. Because link reference are stripped during
        // rendering, the unique link is present in the rendered version if and only
        // if the match at its offset was in fact rendered as a link or image.
        var complete = chunk.before + chunk.selection + chunk.after;
        var rendered = this.converter.makeHtml(complete);
        var testlink = "http://this-is-a-real-link.biz/";
        
        // If our fake link appears in the rendered version *before* we have added it,
        // this probably means you're a Meta Stack Exchange user who is deliberately
        // trying to break this feature. You can still break this workaround if you
        // attach a plugin to the converter that sometimes (!) inserts this link. In
        // that case, consider yourself unsupported.
        while (rendered.indexOf(testlink) != -1)
            testlink += "nicetry/";
        
        var fakedefs = "\n\n";

        var uniquified = complete.replace(regex, function uniquify(wholeMatch, id, offset) {
            fakedefs += " [" + offset + "]: " + testlink + offset + "/unicorn\n";
            return "[" + offset + "]";
        });
        
        rendered = this.converter.makeHtml(uniquified + fakedefs);
        
        var okayToModify = function(offset) {
            return rendered.indexOf(testlink + offset + "/unicorn") !== -1;
        }
        
        // property names are "L_" + link (prefixed to prevent collisions with built-in properties),
        // values are the definition numbers
        var addedDefsByUrl = {};
        var addOrReuseDefNumber = function (def) {
            var stripped = def.replace(/^[ ]{0,3}\[(\d+)\]:/, "");
            var key = "L_" + stripped;
            if (key in addedDefsByUrl)
                return addedDefsByUrl[key];
            refNumber++;
            def = "  [" + refNumber + "]:" + stripped;
            defs += "\n" + def;
            addedDefsByUrl[key] = refNumber;
            return refNumber;
        };

        // the regex is tested on the (up to) three chunks separately,
        // so in order to have the correct offsets to check against okayToModify(), we
        // have to keep track of how many characters are in the original source before
        // the substring that we're looking at. Note that doLinkOrImage aligns the selection
        // on potential brackets, so there should be no major breakage from the chunk
        // separation.
        var skippedChars = 0;

        // note that
        // a) the recursive call to getLink cannot go infinite, because by definition
        //    of regex, inner is always a proper substring of wholeMatch, and
        // b) more than one level of nesting is neither supported by the regex
        //    nor making a lot of sense (the only use case for nesting is a linked image)
        var getLink = function (wholeMatch, id, offset) {
            if (!okayToModify(skippedChars + offset))
                return wholeMatch;
            if (defsToAdd[id]) {
                var refnum = addOrReuseDefNumber(defsToAdd[id]);
                return "[" + refnum + "]";
            }
            return wholeMatch;
        };

        var len = chunk.before.length;
        chunk.before = chunk.before.replace(regex, getLink);
        skippedChars += len;
        
        len = chunk.selection.length;
        var refOut;
        if (linkDef) {
            refOut = addOrReuseDefNumber(linkDef);
        }
        else {
            chunk.selection = chunk.selection.replace(regex, getLink);
        }
        skippedChars += len;        

        chunk.after = chunk.after.replace(regex, getLink);

        if (chunk.after) {
            chunk.after = chunk.after.replace(/\n*$/, "");
        }
        if (!chunk.after) {
            chunk.selection = chunk.selection.replace(/\n*$/, "");
        }

        chunk.after += "\n\n" + defs;

        return refOut;
    };

    // takes the line as entered into the add link/as image dialog and makes
    // sure the URL and the optinal title are "nice".
    function properlyEncoded(linkdef) {
        return linkdef.replace(/^\s*(.*?)(?:\s+"(.+)")?\s*$/, function (wholematch, link, title) {
            
            var inQueryString = false;

            // Having `[^\w\d-./]` in there is just a shortcut that lets us skip
            // the most common characters in URLs. Replacing that it with `.` would not change
            // the result, because encodeURI returns those characters unchanged, but it
            // would mean lots of unnecessary replacement calls. Having `[` and `]` in that
            // section as well means we do *not* enocde square brackets. These characters are
            // a strange beast in URLs, but if anything, this causes URLs to be more readable,
            // and we leave it to the browser to make sure that these links are handled without
            // problems.
            link = link.replace(/%(?:[\da-fA-F]{2})|\?|\+|[^\w\d-./[\]]/g, function (match) {
                // Valid percent encoding. Could just return it as is, but we follow RFC3986
                // Section 2.1 which says "For consistency, URI producers and normalizers
                // should use uppercase hexadecimal digits for all percent-encodings."
                // Note that we also handle (illegal) stand-alone percent characters by
                // replacing them with "%25"
                if (match.length === 3 && match.charAt(0) == "%") {
                    return match.toUpperCase();
                }
                switch (match) {
                    case "?":
                        inQueryString = true;
                        return "?";
                        break;
                    
                    // In the query string, a plus and a space are identical -- normalize.
                    // Not strictly necessary, but identical behavior to the previous version
                    // of this function.
                    case "+":
                        if (inQueryString)
                            return "%20";
                        break;
                }
                return encodeURI(match);
            })
            
            if (title) {
                title = title.trim ? title.trim() : title.replace(/^\s*/, "").replace(/\s*$/, "");
                title = title.replace(/"/g, "quot;").replace(/\(/g, "&#40;").replace(/\)/g, "&#41;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
            }
            return title ? link + ' "' + title + '"' : link;
        });
    }

    commandProto.doLinkOrImage = function (chunk, postProcessing, isImage) {

        chunk.trimWhitespace();
        chunk.findTags(/\s*!?\[/, /\][ ]?(?:\n[ ]*)?(\[.*?\])?/);
        var background;
        var wrapImageInLink = this.wrapImageInLink;
        var convertImagesToLinks = this.convertImagesToLinks;

        if (chunk.endTag.length > 1 && chunk.startTag.length > 0) {

            chunk.startTag = chunk.startTag.replace(/!?\[/, "");
            chunk.endTag = "";
            this.addLinkDef(chunk, null);

        }
        else {
            
            // We're moving start and end tag back into the selection, since (as we're in the else block) we're not
            // *removing* a link, but *adding* one, so whatever findTags() found is now back to being part of the
            // link text. linkEnteredCallback takes care of escaping any brackets.
            chunk.selection = chunk.startTag + chunk.selection + chunk.endTag;
            chunk.startTag = chunk.endTag = "";

            if (/\n\n/.test(chunk.selection)) {
                this.addLinkDef(chunk, null);
                return;
            }
            var that = this;
            // The function to be executed when you enter a link and press OK or Cancel.
            // Marks up the link and adds the ref.
            var linkEnteredCallback = function (link) {

                background.parentNode.removeChild(background);

                if (link !== null) {
                    // (                          $1
                    //     [^\\]                  anything that's not a backslash
                    //     (?:\\\\)*              an even number (this includes zero) of backslashes
                    // )
                    // (?=                        followed by
                    //     [[\]]                  an opening or closing bracket
                    // )
                    //
                    // In other words, a non-escaped bracket. These have to be escaped now to make sure they
                    // don't count as the end of the link or similar.
                    // Note that the actual bracket has to be a lookahead, because (in case of to subsequent brackets),
                    // the bracket in one match may be the "not a backslash" character in the next match, so it
                    // should not be consumed by the first match.
                    // The "prepend a space and finally remove it" steps makes sure there is a "not a backslash" at the
                    // start of the string, so this also works if the selection begins with a bracket. We cannot solve
                    // this by anchoring with ^, because in the case that the selection starts with two brackets, this
                    // would mean a zero-width match at the start. Since zero-width matches advance the string position,
                    // the first bracket could then not act as the "not a backslash" for the second.
                    chunk.selection = (" " + chunk.selection).replace(/([^\\](?:\\\\)*)(?=[[\]])/g, "$1\\").substr(1);
                    
                    var linkDef = " [999]: " + properlyEncoded(link);

                    var num = that.addLinkDef(chunk, linkDef);
                    if (!isImage || (wrapImageInLink && !convertImagesToLinks))
                    {
                        chunk.startTag = "[";
                        chunk.endTag = "][" + num + "]";
                    }
                    if (isImage)
                    {
                        if (!convertImagesToLinks) {
                            chunk.startTag += "![";
                        } else {
                            chunk.startTag += "[";
                        }
                        chunk.endTag = "][" + num + "]" + chunk.endTag;
                    }

                    if (!chunk.selection) {
                        if (isImage) {
                            chunk.selection = that.getString("imagedescription");
                        }
                        else {
                            chunk.selection = that.getString("linkdescription");
                        }
                    }

                    if (isImage && convertImagesToLinks) {
                        that.hooks.imageConvertedToLink();
                    }
                }
                postProcessing();
            };

            background = ui.createBackground();

            if (isImage) {
                if (!this.hooks.insertImageDialog(linkEnteredCallback))
                    ui.prompt(this.getString("imagedialog"), imageDefaultText, this.getString("ok"), this.getString("cancel"), linkEnteredCallback);
            }
            else {
                if (!this.hooks.insertLinkDialog(linkEnteredCallback))
                    ui.prompt(this.getString("linkdialog"), linkDefaultText, this.getString("ok"), this.getString("cancel"), linkEnteredCallback);
            }
            return true;
        }
    };

    // When making a list, hitting shift-enter will put your cursor on the next line
    // at the current indent level.
    commandProto.doAutoindent = function (chunk, postProcessing) {

        var commandMgr = this,
            fakeSelection = false;

        chunk.before = chunk.before.replace(/(\n|^)[ ]{0,3}([*+-]|\d+[.])[ \t]*\n$/, "\n\n");
        chunk.before = chunk.before.replace(/(\n|^)[ ]{0,3}>[ \t]*\n$/, "\n\n");
        chunk.before = chunk.before.replace(/(\n|^)[ \t]+\n$/, "\n\n");
        
        // There's no selection, end the cursor wasn't at the end of the line:
        // The user wants to split the current list item / code line / blockquote line
        // (for the latter it doesn't really matter) in two. Temporarily select the
        // (rest of the) line to achieve this.
        if (!chunk.selection && !/^[ \t]*(?:\n|$)/.test(chunk.after)) {
            chunk.after = chunk.after.replace(/^[^\n]*/, function (wholeMatch) {
                chunk.selection = wholeMatch;
                return "";
            });
            fakeSelection = true;
        }

        if (/(\n|^)[ ]{0,3}([*+-]|\d+[.])[ \t]+.*\n$/.test(chunk.before)) {
            if (commandMgr.doList) {
                commandMgr.doList(chunk);
            }
        }
        if (/(\n|^)[ ]{0,3}>[ \t]+.*\n$/.test(chunk.before)) {
            if (commandMgr.doBlockquote) {
                commandMgr.doBlockquote(chunk);
            }
        }
        if (/(\n|^)(\t|[ ]{4,}).*\n$/.test(chunk.before)) {
            if (commandMgr.doCode) {
                commandMgr.doCode(chunk);
            }
        }
        
        if (fakeSelection) {
            chunk.after = chunk.selection + chunk.after;
            chunk.selection = "";
        }
    };

    commandProto.doBlockquote = function (chunk, postProcessing) {

        chunk.selection = chunk.selection.replace(/^(\n*)([^\r]+?)(\n*)$/,
            function (totalMatch, newlinesBefore, text, newlinesAfter) {
                chunk.before += newlinesBefore;
                chunk.after = newlinesAfter + chunk.after;
                return text;
            });

        chunk.before = chunk.before.replace(/(>[ \t]*)$/,
            function (totalMatch, blankLine) {
                chunk.selection = blankLine + chunk.selection;
                return "";
            });

        chunk.selection = chunk.selection.replace(/^(\s|>)+$/, "");
        chunk.selection = chunk.selection || this.getString("quoteexample");

        // The original code uses a regular expression to find out how much of the
        // text *directly before* the selection already was a blockquote:

        /*
        if (chunk.before) {
        chunk.before = chunk.before.replace(/\n?$/, "\n");
        }
        chunk.before = chunk.before.replace(/(((\n|^)(\n[ \t]*)*>(.+\n)*.*)+(\n[ \t]*)*$)/,
        function (totalMatch) {
        chunk.startTag = totalMatch;
        return "";
        });
        */

        // This comes down to:
        // Go backwards as many lines a possible, such that each line
        //  a) starts with ">", or
        //  b) is almost empty, except for whitespace, or
        //  c) is preceded by an unbroken chain of non-empty lines
        //     leading up to a line that starts with ">" and at least one more character
        // and in addition
        //  d) at least one line fulfills a)
        //
        // Since this is essentially a backwards-moving regex, it's susceptible to
        // catstrophic backtracking and can cause the browser to hang;
        // see e.g. http://meta.stackexchange.com/questions/9807.
        //
        // Hence we replaced this by a simple state machine that just goes through the
        // lines and checks for a), b), and c).

        var match = "",
            leftOver = "",
            line;
        if (chunk.before) {
            var lines = chunk.before.replace(/\n$/, "").split("\n");
            var inChain = false;
            for (var i = 0; i < lines.length; i++) {
                var good = false;
                line = lines[i];
                inChain = inChain && line.length > 0; // c) any non-empty line continues the chain
                if (/^>/.test(line)) {                // a)
                    good = true;
                    if (!inChain && line.length > 1)  // c) any line that starts with ">" and has at least one more character starts the chain
                        inChain = true;
                } else if (/^[ \t]*$/.test(line)) {   // b)
                    good = true;
                } else {
                    good = inChain;                   // c) the line is not empty and does not start with ">", so it matches if and only if we're in the chain
                }
                if (good) {
                    match += line + "\n";
                } else {
                    leftOver += match + line;
                    match = "\n";
                }
            }
            if (!/(^|\n)>/.test(match)) {             // d)
                leftOver += match;
                match = "";
            }
        }

        chunk.startTag = match;
        chunk.before = leftOver;

        // end of change

        if (chunk.after) {
            chunk.after = chunk.after.replace(/^\n?/, "\n");
        }

        chunk.after = chunk.after.replace(/^(((\n|^)(\n[ \t]*)*>(.+\n)*.*)+(\n[ \t]*)*)/,
            function (totalMatch) {
                chunk.endTag = totalMatch;
                return "";
            }
        );

        var replaceBlanksInTags = function (useBracket) {

            var replacement = useBracket ? "> " : "";

            if (chunk.startTag) {
                chunk.startTag = chunk.startTag.replace(/\n((>|\s)*)\n$/,
                    function (totalMatch, markdown) {
                        return "\n" + markdown.replace(/^[ ]{0,3}>?[ \t]*$/gm, replacement) + "\n";
                    });
            }
            if (chunk.endTag) {
                chunk.endTag = chunk.endTag.replace(/^\n((>|\s)*)\n/,
                    function (totalMatch, markdown) {
                        return "\n" + markdown.replace(/^[ ]{0,3}>?[ \t]*$/gm, replacement) + "\n";
                    });
            }
        };

        if (/^(?![ ]{0,3}>)/m.test(chunk.selection)) {
            this.wrap(chunk, SETTINGS.lineLength - 2);
            chunk.selection = chunk.selection.replace(/^/gm, "> ");
            replaceBlanksInTags(true);
            chunk.skipLines();
        } else {
            chunk.selection = chunk.selection.replace(/^[ ]{0,3}> ?/gm, "");
            this.unwrap(chunk);
            replaceBlanksInTags(false);

            if (!/^(\n|^)[ ]{0,3}>/.test(chunk.selection) && chunk.startTag) {
                chunk.startTag = chunk.startTag.replace(/\n{0,2}$/, "\n\n");
            }

            if (!/(\n|^)[ ]{0,3}>.*$/.test(chunk.selection) && chunk.endTag) {
                chunk.endTag = chunk.endTag.replace(/^\n{0,2}/, "\n\n");
            }
        }

        chunk.selection = this.hooks.postBlockquoteCreation(chunk.selection);

        if (!/\n/.test(chunk.selection)) {
            chunk.selection = chunk.selection.replace(/^(> *)/,
            function (wholeMatch, blanks) {
                chunk.startTag += blanks;
                return "";
            });
        }
    };

    commandProto.doCode = function (chunk, postProcessing) {

        var hasTextBefore = /\S[ ]*$/.test(chunk.before);
        var hasTextAfter = /^[ ]*\S/.test(chunk.after);

        // Use 'four space' markdown if the selection is on its own
        // line or is multiline.
        if ((!hasTextAfter && !hasTextBefore) || /\n/.test(chunk.selection)) {

            chunk.before = chunk.before.replace(/[ ]{4}$/,
                function (totalMatch) {
                    chunk.selection = totalMatch + chunk.selection;
                    return "";
                });

            var nLinesBack = 1;
            var nLinesForward = 1;

            if (/(\n|^)(\t|[ ]{4,}).*\n$/.test(chunk.before)) {
                nLinesBack = 0;
            }
            if (/^\n(\t|[ ]{4,})/.test(chunk.after)) {
                nLinesForward = 0;
            }

            chunk.skipLines(nLinesBack, nLinesForward);

            if (!chunk.selection) {
                chunk.startTag = "    ";
                chunk.selection = this.getString("codeexample");
            }
            else {
                if (/^[ ]{0,3}\S/m.test(chunk.selection)) {
                    if (/\n/.test(chunk.selection))
                        chunk.selection = chunk.selection.replace(/^/gm, "    ");
                    else // if it's not multiline, do not select the four added spaces; this is more consistent with the doList behavior
                        chunk.before += "    ";
                }
                else {
                    chunk.selection = chunk.selection.replace(/^(?:[ ]{4}|[ ]{0,3}\t)/gm, "");
                }
            }
        }
        else {
            // Use backticks (`) to delimit the code block.

            chunk.trimWhitespace();
            chunk.findTags(/`/, /`/);

            if (!chunk.startTag && !chunk.endTag) {
                chunk.startTag = chunk.endTag = "`";
                if (!chunk.selection) {
                    chunk.selection = this.getString("codeexample");
                }
            }
            else if (chunk.endTag && !chunk.startTag) {
                chunk.before += chunk.endTag;
                chunk.endTag = "";
            }
            else {
                chunk.startTag = chunk.endTag = "";
            }
        }
    };

    commandProto.doList = function (chunk, postProcessing, isNumberedList) {

        // These are identical except at the very beginning and end.
        // Should probably use the regex extension function to make this clearer.
        var previousItemsRegex = /(\n|^)(([ ]{0,3}([*+-]|\d+[.])[ \t]+.*)(\n.+|\n{2,}([*+-].*|\d+[.])[ \t]+.*|\n{2,}[ \t]+\S.*)*)\n*$/;
        var nextItemsRegex = /^\n*(([ ]{0,3}([*+-]|\d+[.])[ \t]+.*)(\n.+|\n{2,}([*+-].*|\d+[.])[ \t]+.*|\n{2,}[ \t]+\S.*)*)\n*/;

        // The default bullet is a dash but others are possible.
        // This has nothing to do with the particular HTML bullet,
        // it's just a markdown bullet.
        var bullet = "-";

        // The number in a numbered list.
        var num = 1;

        // Get the item prefix - e.g. " 1. " for a numbered list, " - " for a bulleted list.
        var getItemPrefix = function () {
            var prefix;
            if (isNumberedList) {
                prefix = " " + num + ". ";
                num++;
            }
            else {
                prefix = " " + bullet + " ";
            }
            return prefix;
        };

        // Fixes the prefixes of the other list items.
        var getPrefixedItem = function (itemText) {

            // The numbering flag is unset when called by autoindent.
            if (isNumberedList === undefined) {
                isNumberedList = /^\s*\d/.test(itemText);
            }

            // Renumber/bullet the list element.
            itemText = itemText.replace(/^[ ]{0,3}([*+-]|\d+[.])\s/gm,
                function (_) {
                    return getItemPrefix();
                });

            return itemText;
        };

        chunk.findTags(/(\n|^)*[ ]{0,3}([*+-]|\d+[.])\s+/, null);

        if (chunk.before && !/\n$/.test(chunk.before) && !/^\n/.test(chunk.startTag)) {
            chunk.before += chunk.startTag;
            chunk.startTag = "";
        }

        if (chunk.startTag) {

            var hasDigits = /\d+[.]/.test(chunk.startTag);
            chunk.startTag = "";
            chunk.selection = chunk.selection.replace(/\n[ ]{4}/g, "\n");
            this.unwrap(chunk);
            chunk.skipLines();

            if (hasDigits) {
                // Have to renumber the bullet points if this is a numbered list.
                chunk.after = chunk.after.replace(nextItemsRegex, getPrefixedItem);
            }
            if (isNumberedList == hasDigits) {
                return;
            }
        }

        var nLinesUp = 1;

        chunk.before = chunk.before.replace(previousItemsRegex,
            function (itemText) {
                if (/^\s*([*+-])/.test(itemText)) {
                    bullet = re.$1;
                }
                nLinesUp = /[^\n]\n\n[^\n]/.test(itemText) ? 1 : 0;
                return getPrefixedItem(itemText);
            });

        if (!chunk.selection) {
            chunk.selection = this.getString("litem");
        }

        var prefix = getItemPrefix();

        var nLinesDown = 1;

        chunk.after = chunk.after.replace(nextItemsRegex,
            function (itemText) {
                nLinesDown = /[^\n]\n\n[^\n]/.test(itemText) ? 1 : 0;
                return getPrefixedItem(itemText);
            });

        chunk.trimWhitespace(true);
        chunk.skipLines(nLinesUp, nLinesDown, true);
        chunk.startTag = prefix;
        var spaces = prefix.replace(/./g, " ");
        this.wrap(chunk, SETTINGS.lineLength - spaces.length);
        chunk.selection = chunk.selection.replace(/\n/g, "\n" + spaces);

    };

    commandProto.doHeading = function (chunk, postProcessing) {

        // Remove leading/trailing whitespace and reduce internal spaces to single spaces.
        chunk.selection = chunk.selection.replace(/\s+/g, " ");
        chunk.selection = chunk.selection.replace(/(^\s+|\s+$)/g, "");

        // If we clicked the button with no selected text, we just
        // make a level 2 hash header around some default text.
        if (!chunk.selection) {
            chunk.startTag = "## ";
            chunk.selection = this.getString("headingexample");
            chunk.endTag = " ##";
            return;
        }

        var headerLevel = 0;     // The existing header level of the selected text.

        // Remove any existing hash heading markdown and save the header level.
        chunk.findTags(/#+[ ]*/, /[ ]*#+/);
        if (/#+/.test(chunk.startTag)) {
            headerLevel = re.lastMatch.length;
        }
        chunk.startTag = chunk.endTag = "";

        // Try to get the current header level by looking for - and = in the line
        // below the selection.
        chunk.findTags(null, /\s?(-+|=+)/);
        if (/=+/.test(chunk.endTag)) {
            headerLevel = 1;
        }
        if (/-+/.test(chunk.endTag)) {
            headerLevel = 2;
        }

        // Skip to the next line so we can create the header markdown.
        chunk.startTag = chunk.endTag = "";
        chunk.skipLines(1, 1);

        // We make a level 2 header if there is no current header.
        // If there is a header level, we subtract one from the header level.
        // If it's already a level 1 header, it's removed.
        var headerLevelToCreate = headerLevel == 0 ? 2 : headerLevel - 1;

        if (headerLevelToCreate > 0) {

            // The button only creates level 1 and 2 underline headers.
            // Why not have it iterate over hash header levels?  Wouldn't that be easier and cleaner?
            var headerChar = headerLevelToCreate >= 2 ? "-" : "=";
            var len = chunk.selection.length;
            if (len > SETTINGS.lineLength) {
                len = SETTINGS.lineLength;
            }
            chunk.endTag = "\n";
            while (len--) {
                chunk.endTag += headerChar;
            }
        }
    };

    commandProto.doHorizontalRule = function (chunk, postProcessing) {
        chunk.startTag = "----------\n";
        chunk.selection = "";
        chunk.skipLines(2, 1, true);
    }


})();