Provide content input

[noyainrain]

Provide a text area with the ability to add web content (like a link, image or video). For convenience, if URL input is detected, show a preview along with the option to discard it.

[noyainrain]

A temporary workaround to prevent a link preview is to insert a single space before the URL (currently a URL is only recognized at the very beginning of the text).

[noyainrain]

Server draft:

Previews
--------

Web :ref:`Resource` previews.

.. http:get:: /api/previews/(url)

   Get a description of the web :ref:`Resource` at *url*.

Client draft:

/**
 * Input for text and web :ref:`Resource` content.
 *
 * For convenience, when a URL is entered, the web resource is attached automatically.
 */
micro.compoments.contentinput.ContentInputElement = class extends HTMLElement {
    /**
     * Current value as object ``{text, resource}``.
     *
     * *text* is the text and *resource* the web :ref:`Resource` content. May both be ``null``.
     */
    get valueAsObject() {}

    /** See :attr:`HTMLInputElement.required`. */
    get required() {}

    /** See :attr:`HTMLInputElement.placeholder`. */
    get placeholder() {}

    /** Attach the web resource at *url*. */
    async attach(url) {}
};

/**
 * Extension for an input that detects when a URL is entered.
 *
 * .. attribute:: input
 *
 *    Extended :class:`HTMLInputElement` or :class:`HTMLTextAreaElement`.
 *
 * .. describe:: onurlinput
 *
 *    Event handler for ``urlinput``, dispatched when a *url* is entered.
 */
micro.compoments.contentinput.URLDetection = class {
    constructor(input) {}
};

UI draft: