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Add documentation in vimdoc format

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+*easytags.txt* Automated tag generation and syntax highlighting in Vim
+
+Vim has long been my favorite text editor and combined with Exuberant Ctags
+[1] it has the potential to provide most of what I expect from an integrated
+development environment [2]. Exuberant Ctags is the latest incarnation of a
+family of computer programs [3] that scan source code files to create an index
+of identifiers (tags) and where they are defined. Vim uses this index (a
+so-called tags file) to enable you to jump to the definition of any identifier
+using the Control-] (see |CTRL-]|) mapping.
+
+When you're familiar with integrated development environments you may
+recognize this feature as "Go-to definition". One advantage of the combination
+of Vim and Exuberant Ctags over integrated development environments is that
+Vim supports syntax highlighting for over 500 file types [4] (!) and Exuberant
+Ctags can generate tags for over 40 file types [5] as well...
+
+There's just one problem: You have to manually keep your tags files up-to-date
+and this turns out to be a royal pain in the ass! So I set out to write a Vim
+plug-in that would do this boring work for me. When I finished the plug-in's
+basic functionality (one automatic command and a call to |system()| later) I
+became interested in dynamic syntax highlighting, so I added that as well to
+see if it would work -- surprisingly well I'm happy to report!
+
+==============================================================================
+Install & usage ~
+
+Unzip the most recent ZIP archive [6] file inside your Vim profile directory
+(usually this is '~/.vim' on UNIX and '%USERPROFILE%\vimfiles' on Windows),
+restart Vim and execute the command ':helptags ~/.vim/doc' (use ':helptags
+~\vimfiles\doc' instead on Windows). Now try it out: Edit any file type
+supported by Exuberant Ctags and within ten seconds the plug-in should
+create/update your tags file ('~/.vimtags' on UNIX, '~/_vimtags' on Windows)
+with the tags defined in the file you just edited! This means that whatever
+file you're editing in Vim (as long as it's on the local file system), tags
+will always be available by the time you need them!
+
+Additionally if the file you just opened is a C, C++, Objective-C, Java, Lua,
+Python, PHP or Vim source file you should also notice that the function and
+type names defined in the file have been syntax highlighted.
+
+The 'easytags.vim' plug-in is intended to work automatically once it's
+installed, but if you want to change how it works there are several options
+you can change and commands you can execute from your own mappings and/or
+automatic commands. These are all documented below.
+
+Note that if the plug-in warns you 'ctags' isn't installed you'll have to
+download it from its homepage [1], or if you're running Debian/Ubuntu you can
+install it by executing the following shell command:
+>
+ $ sudo apt-get install exuberant-ctags
+
+------------------------------------------------------------------------------
+If you're using Windows ~
+
+On Windows the |system()| function used by 'easytags.vim' causes a command
+prompt window to pop up while Exuberant Ctags is executing. If this bothers
+you then you can install my shell.vim [7] plug-in which includes a DLL [8]
+that works around this issue. Once you've installed both plug-ins it should
+work out of the box! Please let me know if this doesn't work for you.
+
+------------------------------------------------------------------------------
+The *:UpdateTags* command
+
+This command executes Exuberant Ctags [1] from inside Vim to update the global
+tags file defined by |g:easytags_file|. When no arguments are given the tags for
+the current file are updated, otherwise the arguments are passed on to
+'ctags'. For example when you execute the Vim command ':UpdateTags -R ~/.vim'
+(or ':UpdateTags -R ~\vimfiles' on Windows) the plug-in will execute 'ctags -R
+~/.vim' for you (with some additional arguments, see the troubleshooting
+section ":HighlightTags only works for the tags file created by |:UpdateTags|"
+for more information).
+
+When you execute this command like |:UpdateTags|! (including the bang!) then all
+tags whose files are missing will be filtered from the global tags file.
+
+Note that this command will be executed automatically every once in a while,
+assuming you haven't changed |g:easytags_on_cursorhold|.
+
+------------------------------------------------------------------------------
+The *:HighlightTags* command
+
+When you execute this command while editing one of the supported file types
+(see above) the relevant tags in the current file are highlighted. The tags to
+highlight are gathered from all tags files known to Vim (through the |'tags'|
+option).
+
+Note that this command will be executed automatically every once in a while,
+assuming you haven't changed |g:easytags_on_cursorhold|.
+
+------------------------------------------------------------------------------
+The *g:easytags_cmd* option
+
+The plug-in will try to determine the location where Exuberant Ctags is
+installed on its own but this might not always work because any given
+executable named 'ctags' in your '$PATH' might not in fact be Exuberant Ctags
+but some older, more primitive 'ctags' implementation which doesn't support
+the same command line options and thus breaks the 'easytags.vim' plug-in. If
+this is the case you can set the global variable |g:easytags_cmd| to the
+location where you've installed Exuberant Ctags, e.g.:
+>
+ :let g:easytags_cmd = '/usr/local/bin/ctags'
+
+------------------------------------------------------------------------------
+The *g:easytags_file* option
+
+As mentioned above the plug-in will store your tags in '~/.vimtags' on UNIX
+and '~/_vimtags' on Windows. To change the location of this file, set the
+global variable |g:easytags_file|, e.g.:
+>
+ :let g:easytags_file = '~/.vim/tags'
+
+A leading '~' in the |g:easytags_file| variable is expanded to your current home
+directory ('$HOME' on UNIX, '%USERPROFILE%' on Windows).
+
+------------------------------------------------------------------------------
+The *g:easytags_always_enabled* option
+
+By default the plug-in automatically generates and highlights tags when you
+stop typing for a few seconds (this works using the |CursorHold| automatic
+command). This means that when you edit a file, the dynamic highlighting won't
+appear until you pause for a moment. If you don't like this you can configure
+the plug-in to always enable dynamic highlighting:
+>
+ :let g:easytags_always_enabled = 1
+
+Be warned that after setting this option you'll probably notice why it's
+disabled by default: Every time you edit a file in Vim, the plug-in will first
+run Exuberant Ctags and then highlight the tags, and this slows Vim down quite
+a lot. I have some ideas on how to improve this latency by running Exuberant
+Ctags in the background so stay tuned!
+
+Note: If you change this option it won't apply until you restart Vim, so
+you'll have to set this option in your |vimrc| script.
+
+------------------------------------------------------------------------------
+The *g:easytags_on_cursorhold* option
+
+As I explained above the plug-in by default doesn't update or highlight your
+tags until you stop typing for a moment. The plug-in tries hard to do the
+least amount of work possible in this break but it might still interrupt your
+workflow. If it does you can disable the periodic update:
+>
+ :let g:easytags_on_cursorhold = 0
+
+Note: Like the |g:easytags_always_enabled| option, if you change this option it
+won't apply until you restart Vim, so you'll have to set this option in your
+|vimrc| script.
+
+------------------------------------------------------------------------------
+The *g:easytags_autorecurse* option
+
+When the |:UpdateTags| command is executed automatically or without arguments,
+it defaults to updating just the tags for the current file. If you'd rather
+have it recursively scan everything below the directory of the current file
+then set this option to true (1):
+>
+ :let g:easytags_autorecurse = 1
+
+You have to explicitly enable this option because it should only be used while
+navigating around small directory trees. Imagine always having this option
+enabled and then having to edit a file in e.g. the root of your home
+directory: The 'easytags.vim' plug-in would freeze Vim for a long time while
+you'd have to wait for Exuberant Cags to scan thousands of files...
+
+Note that when you enable this option the 'easytags.vim' plug-in might ignore
+other options like |g:easytags_resolve_links|. This is an implementation detail
+which I intend to fix.
+
+------------------------------------------------------------------------------
+The *g:easytags_include_members* option
+
+Exuberant Ctags knows how to generate tags for struct/class members in C++ and
+Java source code but doesn't do so by default because it can more than double
+the size of your tags files, thus taking much longer to read/write the tags
+file. When you enable the |g:easytags_include_members| option from your |vimrc|
+script (before the 'easytags.vim' plug-in is loaded):
+>
+ :let g:easytags_include_members = 1
+
+Exuberant Ctags will be instructed to include struct/class members using the
+'--extra=+q' command line argument and the 'easytags.vim' plug-in will
+highlight them using the 'cMember' highlighting group. Because most color
+schemes don't distinguish the Identifier and Type (see |group-name|)
+highlighting groups all members will now probably look like type definitions.
+You can change that by executing either of the following Vim commands (from
+your vimrc script, a file type plug-in, etc.):
+>
+ " If you like one of the existing styles you can link them:
+ highlight link cMember Special
+>
+ " You can also define your own style if you want:
+ highlight cMember gui=italic
+
+------------------------------------------------------------------------------
+The *g:easytags_resolve_links* option
+
+UNIX has symbolic links [9] and hard links [10], both of which conflict with
+the concept of having one unique location for every identifier. With regards
+to hard links there's not much anyone can do, but because I use symbolic links
+quite a lot I've added this option. It's disabled by default since it has a
+small performance impact and might not do what unknowing users expect it to:
+When you enable this option the plug-in will resolve symbolic links in
+pathnames, which means your tags file will only contain entries with canonical
+pathnames [11]. To enable this option (which I strongly suggest doing when you
+run UNIX and use symbolic links) execute the following Vim command:
+>
+ :let g:easytags_resolve_links = 1
+
+------------------------------------------------------------------------------
+The *g:easytags_suppress_ctags_warning* option
+
+If this is set and not false, it will suppress the warning on startup if ctags
+is not found or not recent enough.
+>
+ :let g:easytags_suppress_ctags_warning = 1
+
+------------------------------------------------------------------------------
+How to customize the highlighting colors? ~
+
+The easytags plug-in defines new highlighting groups for dynamically
+highlighted tags. These groups are linked to Vim's default groups so that
+they're colored out of the box, but if you want you can change the styles. To
+do so use a 'highlight' command such as the ones given a few paragraphs back.
+Of course you'll need to change the group name. Here are the group names used
+by the easytags plug-in:
+
+ * Lua: 'luaFuncTag'
+ * C: 'cTypeTag', 'cEnumTag', 'cPreProcTag', 'cFunctionTag', 'cMemberTag'
+ * PHP: 'phpFunctionsTag', 'phpClassesTag'
+ * Vim: 'vimAutoGroupTag', 'vimCommandTag', 'vimFuncNameTag',
+ 'vimScriptFuncNameTag'
+ * Python: 'pythonFunctionTag', 'pythonMethodTag', 'pythonClassTag'
+ * Java: 'javaClassTag', 'javaMethodTag'
+ * C#: 'csClassOrStructTag', 'csMethodTag'
+
+As you can see each of these names ends in 'Tag' to avoid conflicts with the
+syntax modes shipped with Vim. And about the singular/plural confusion: I've
+tried to match the existing highlighting groups defined by popular syntax
+modes (except of course for the 'Tag' suffix).
+
+==============================================================================
+Troubleshooting ~
+
+------------------------------------------------------------------------------
+:HighlightTags only works for the tags file created by :UpdateTags ~
+
+If you want to create tags files and have their tags highlighted by the
+'easytags.vim' plug-in then you'll have to create the tags file with certain
+arguments to Exuberant Ctags:
+>
+ $ ctags --fields=+l --c-kinds=+p --c++-kinds=+p ...
+
+The '--fields=+l' argument makes sure that Exuberant Ctags includes a
+'language:...' property with each entry in the tags file. This is required by
+the |:HighlightTags| command so it can filter tags by their file type. The other
+two arguments make sure Exuberant Ctags generates tags for function prototypes
+in C/C++ source code.
+
+If you have the |g:easytags_include_members| option enabled (its off by default)
+then you'll also need to add the '--extra=+q' argument so that Exuberant Ctags
+generates tags for structure/class members.
+
+------------------------------------------------------------------------------
+The plug-in complains that Exuberant Ctags isn't installed ~
+
+After a Mac OS X user found out the hard way that the 'ctags' executable isn't
+always Exuberant Ctags and we spend a few hours debugging the problem I added
+proper version detection: The plug-in executes 'ctags --version' when Vim is
+started to verify that Exuberant Ctags 5.5 or newer is installed. If it isn't
+Vim will show the following message on startup:
+>
+ easytags.vim: Plug-in not loaded because Exuberant Ctags isn't installed!
+ Please download & install Exuberant Ctags from http://ctags.sf.net
+
+If the installed Exuberant Ctags version is too old the plug-in will complain:
+>
+ easytags.vim: Plug-in not loaded because Exuberant Ctags 5.5
+ or newer is required while you have version %s installed!
+
+If you have the right version of Exuberant Ctags installed but the plug-in
+still complains, try executing the following command from inside Vim:
+>
+ :!which ctags
+
+If this doesn't print the location where you installed Exuberant Ctags it
+means your system already had a 'ctags' executable but it isn't compatible
+with Exuberant Ctags 5.5 and you'll need to set the |g:easytags_cmd| option (see
+above) so the plug-in knows which 'ctags' to run.
+
+------------------------------------------------------------------------------
+Vim locks up while the plug-in is running ~
+
+Once or twice now in several years I've experienced Exuberant Ctags getting
+into an infinite loop when given garbage input. In my case this happened by
+accident a few days ago :-|. Because my plug-in executes 'ctags' in the
+foreground this will block Vim indefinitely! If this happens you might be able
+to kill 'ctags' by pressing Control-C (see |CTRL-C|) but if that doesn't work
+you can also kill it without stopping Vim using a task manager or the 'pkill'
+command (available on most UNIX systems):
+>
+ $ pkill -KILL ctags
+
+If Vim seems very slow and you suspect this plug-in might be the one to blame,
+increase Vim's verbosity level:
+>
+ :set vbs=1
+
+Every time the plug-in executes it will time how long the execution takes and
+add the results to Vim's message history, which you can view by executing the
+|:messages| command.
+
+------------------------------------------------------------------------------
+Failed to highlight tags because pattern is too big! ~
+
+If the 'easytags.vim' plug-in fails to highlight your tags and the error
+message mentions that the pattern is too big, your tags file has grown too
+large for Vim to be able to highlight all tagged identifiers! I've had this
+happen to me with 50 KB patterns because I added most of the headers in
+'/usr/include/' to my tags file. Internally Vim raises the error |E339|: Pattern
+too long and unfortunately the only way to avoid this problem once it occurs
+is to reduce the number of tagged identifiers...
+
+In my case the solution was to move most of the tags from '/usr/include/' over
+to project specific tags files which are automatically loaded by Vim when I
+edit files in different projects because I've set the |'tags'| option as
+follows:
+>
+ :set tags=./.tags;,~/.vimtags
+
+Once you've executed the above command, Vim will automatically look for a file
+named '.tags' in the directory of the current file. Because of the ';' Vim
+also recurses upwards so that you can nest files arbitrarily deep under your
+project directories.
+
+------------------------------------------------------------------------------
+The plug-in doesn't seem to work in Cygwin [12] ~
+
+If you want to use the plug-in with Vim under Cygwin, you need to have the
+Cygwin version of Ctags installed instead of the Windows version (thanks to
+Alex Zuroff for reporting this!).
+
+==============================================================================
+Contact ~
+
+If you have questions, bug reports, suggestions, etc. the author can be
+contacted at peter@peterodding.com. The latest version is available at
+http://peterodding.com/code/vim/easytags/ and http://github.com/xolox/vim-easytags.
+If you like this plug-in please vote for it on Vim Online [13].
+
+==============================================================================
+License ~
+
+This software is licensed under the MIT license [14].
+Copyright 2010 Peter Odding <peter@peterodding.com>.
+
+==============================================================================
+References ~
+
+[1] http://ctags.sourceforge.net/
+[2] http://en.wikipedia.org/wiki/Integrated_development_environment
+[3] http://en.wikipedia.org/wiki/Ctags
+[4] http://ftp.vim.org/vim/runtime/syntax/
+[5] http://ctags.sourceforge.net/languages.html
+[6] http://peterodding.com/code/vim/downloads/easytags
+[7] http://peterodding.com/code/vim/shell/
+[8] http://en.wikipedia.org/wiki/Dynamic-link_library
+[9] http://en.wikipedia.org/wiki/Symbolic_link
+[10] http://en.wikipedia.org/wiki/Hard_link
+[11] http://en.wikipedia.org/wiki/Canonicalization
+[12] http://en.wikipedia.org/wiki/Cygwin
+[13] http://www.vim.org/scripts/script.php?script_id=3114
+[14] http://en.wikipedia.org/wiki/MIT_License
+
+vim: syntax=help nospell
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