Added even more documentation to Element.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "AbstractWorker": {
       "members": {
         "errorEvent": [
           "/**",
           "   * Static factory designed to expose `error` events to event",
           "   * handlers that are not necessarily instances of [AbstractWorker].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
@@ skipping 687 matching lines @@
           "   */"
         ],
         "focusEvent": [
           "/**",
           "   * Static factory designed to expose `focus` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
+        "getBoundingClientRect": [
+          "/**",
+          "   * The smallest bounding rectangle that encompasses this element's padding,",
+          "   * scrollbar, and border.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Element.getBoundingClientRect]",
+          "   * (https://developer.mozilla.org/en-US/docs/Web/API/Element.getBoundingClientRect)",
+          "   * from MDN.",
+          "   * * [The getBoundingClientRect() method]",
+          "   * (http://www.w3.org/TR/cssom-view/#the-getclientrects-and-getboundingclientrect-methods) from W3C.",
+          "   */"
+        ],
+        "getClientRects": [
+          "/**",
+          "   * A list of bounding rectangles for each box associated with this element.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Element.getClientRects]",
+          "   * (https://developer.mozilla.org/en-US/docs/Web/API/Element.getClientRects)",
+          "   * from MDN.",
+          "   * * [The getClientRects() method]",
+          "   * (http://www.w3.org/TR/cssom-view/#the-getclientrects-and-getboundingclientrect-methods) from W3C.",
+          "   */"
+        ],
+        "hidden": [
+          "/**",
+          "   * Indicates whether the element is not relevant to the page's current state.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Hidden attribute specification]",
+          "   * (http://www.whatwg.org/specs/web-apps/current-work/multipage/editing.html#the-hidden-attribute)",
+          "   * from WHATWG.",
+          "   */"
+        ],
         "inputEvent": [
           "/**",
           "   * Static factory designed to expose `input` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
+        "inputMethodContext": [
+          "/**",
+          "   * The current state of IME composition.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Input method editor specification]",
+          "   * (http://www.w3.org/TR/ime-api/) from W3C.",
+          "   */"
+        ],
         "invalidEvent": [
           "/**",
           "   * Static factory designed to expose `invalid` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
         "keydownEvent": [
           "/**",
@@ skipping 328 matching lines @@
           "/// Stream of `fullscreenerror` events handled by this [Element]."
         ],
         "pasteEvent": [
           "/**",
           "   * Static factory designed to expose `paste` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
+        "pseudo": [
+          "/**",
+          "   * The name of this element's custom pseudo-element.",
+          "   *",
+          "   * This value must begin with an x and a hyphen, `x-`, to be considered valid.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Using custom pseudo elements]",
+          "   * (http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom-201/#toc-custom-pseduo)",
+          "   * from HTML5Rocks.",
+          "   * * [Custom pseudo-elements]",
+          "   * (http://www.w3.org/TR/shadow-dom/#custom-pseudo-elements) from W3C.",
+          "   */"
+        ],
         "querySelector": [
           "/**",
           "   * Finds the first descendant element of this element that matches the",
           "   * specified group of selectors.",
           "   *",
           "   * [selectors] should be a string using CSS selector syntax.",
           "   *",
           "   *     // Gets the first descendant with the class 'classname'",
           "   *     var element = element.querySelector('.className');",
           "   *     // Gets the element with id 'id'",
@@ skipping 95 matching lines @@
           "   */"
         ],
         "touchstartEvent": [
           "/**",
           "   * Static factory designed to expose `touchstart` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
+        "translate": [
+          "/**",
+          "   * Specifies whether this element's text content changes when the page is",
+          "   * localized.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [The translate attribute]",
+          "   * (http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#the-translate-attribute)",
+          "   * from WHATWG.",
+          "   */"
+        ],
+        "webkitdropzone": [
+          "/**",
+          "   * A set of space-separated keywords that specify what kind of data this",
+          "   * Element accepts on drop and what to do with that data.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Drag and drop sample]",
+          "   * (https://github.com/dart-lang/dart-samples/tree/master/web/html5/dnd/basics)",
+          "   * based on [the tutorial](http://www.html5rocks.com/en/tutorials/dnd/basics/)",
+          "   * from HTML5Rocks.",
+          "   * * [Drag and drop specification]",
+          "   * (http://www.whatwg.org/specs/web-apps/current-work/multipage/dnd.html#dnd)",
+          "   * from WHATWG.",
+          "   */"
+        ],
         "webkitfullscreenchangeEvent": [
           "/**",
           "   * Static factory designed to expose `fullscreenchange` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
         "webkitfullscreenerrorEvent": [
           "/**",
           "   * Static factory designed to expose `fullscreenerror` events to event",
           "   * handlers that are not necessarily instances of [Element].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
+        ],
+        "webkitRegionOverset": [
+          "/**",
+          "   * The current state of this region.",
+          "   *",
+          "   * If `\"empty\"`, then there is no content in this region.",
+          "   * If `\"fit\"`, then content fits into this region, and more content can be",
+          "   * added. If `\"overset\"`, then there is more content than can be fit into this",
+          "   * region.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [CSS regions and exclusions tutorial]",
+          "   * (http://www.html5rocks.com/en/tutorials/regions/adobe/) from HTML5Rocks.",
+          "   * * [Regions](http://html.adobe.com/webplatform/layout/regions/) from Adobe.",
+          "   * * [CSS regions specification]",
+          "   * (http://www.w3.org/TR/css3-regions/) from W3C.",
+          "   */"
         ]
       }
     },
     "EventSource": {
       "members": {
         "errorEvent": [
           "/**",
           "   * Static factory designed to expose `error` events to event",
           "   * handlers that are not necessarily instances of [EventSource].",
           "   *",
@@ skipping 2918 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }