Element Clear: Apply to all resettable elements

There's no reason to discriminate. We rely on the fact that
the focusing and unfocusing steps are run in order to ensure
that the correct "onchange" event is fired. Existing
implementations based on Selenium's "atoms" don't bother
firing an `input` event, and so neither do we.

As specced, this is a slow-motion way of calling a form's
`reset` method with additional focusing steps. It fulfills
the need of users to reset form fields to their default
values.

Closes #561

Author: shs96c

webdriver-spec.html

@@ -314,6 +314,7 @@ <h3>Dependencies</h3>
    <!-- Replacement enabled --> <li><dfn><a href=https://html.spec.whatwg.org/#replacement-enabled>Replacement enabled</a></dfn>
    <!-- Reset algorithm --><li><dfn><a href=https://html.spec.whatwg.org/#concept-form-reset-control>Reset algorithm</a></dfn>
    <!-- Reset Button --> <li><dfn><a href="https://html.spec.whatwg.org/#reset-button-state-%28type=reset%29">Reset Button</a></dfn> state
+   <!-- Resettable element --> <li><dfn><a href=https://html.spec.whatwg.org/#category-reset>Resettable</a></dfn> element
    <!-- Script execution environment --> <li><dfn><a href=https://html.spec.whatwg.org/#environment>Script execution environment</a></dfn>
    <!-- Script --> <li><dfn><a href=https://html.spec.whatwg.org/#concept-script>Script</a></dfn>
    <!-- Selectedness --> <li><dfn><a href=https://html.spec.whatwg.org/#concept-option-selectedness>Selectedness</a></dfn>
@@ -5297,9 +5298,8 @@ <h3>Element Clear</h3>
 </table>
 
 <p>The <dfn>Element Clear</dfn> <a>command</a>
- <a>scrolls into view</a> an <a>editable</a> <a>element</a>, or
-  an <a><code>input</code> element</a> whose <a><code>type</code>
-  attribute</a> is <a>File</a> and then attempts to clear
+ <a>scrolls into view</a> an <a>editable</a>
+  or <a>resettable</a> <a>element</a> and then attempts to clear
   its <a>selected files</a> or <a>text content</a>.
 
 <p>The <a>remote end steps</a> are:
@@ -5312,8 +5312,9 @@ <h3>Element Clear</h3>
   of <a>trying</a> to <a>get a known element</a>
   with argument <var>element id</var>.
 
- <li><p>If <var>element</var> is not <a>editable</a> return
-  an <a>error</a> with <a>error code</a> <a>invalid element state</a>.
+ <li><p>If <var>element</var> is not <a>editable</a> and is
+  not <a>resettable</a> return an <a>error</a> with <a>error
+  code</a> <a>invalid element state</a>.
 
  <li><p><a>Scroll into view</a> the <var>element</var>.
 
@@ -5330,7 +5331,7 @@ <h3>Element Clear</h3>
 
  <li>If <var>element</var> is <a>content editable</a> follow the steps
   required to <a>clear a content editable element</a>. Otherwise,
-  follow the steps required to <a>clear an editable element</a>.
+  follow the steps required to <a>clear a resettable element</a>.
 
  <li><p>Return <a>success</a> with data <a><code>null</code></a>.
 </ol>
@@ -5347,12 +5348,10 @@ <h3>Element Clear</h3>
  <li><p>Set <var>element</var>'s <a><code>innerHTML</code> IDL
   attribute</a> to an empty string.
 
- <li><p><a>Fire</a> an <a><code>input</code> event</a>.
-
  <li><p>Run the <a>unfocusing steps</a> for the <var>element</var>.
 </ol> <!-- /clearing a content editable element -->
 
-<p>When required to <dfn>clear an editable element</dfn> a <a>remote
+<p>When required to <dfn>clear a resettable element</dfn> a <a>remote
  end</a> must run the following steps:
 
 <ol>
@@ -5363,8 +5362,6 @@ <h3>Element Clear</h3>
 
  <li><p>Run <var>element</var>'s <a>reset algorithm</a>.
 
- <li><p><a>Fire</a> an <a><code>input</code> event</a>.
-
  <li><p>Run the <a>unfocusing steps</a> for the <var>element</var>.
 </ol> <!-- /clearing an editable element -->