Enum-like DOM properties throw TypeErrors on setting to unknown values

As resolved in #547 (comment)

> RESOLUTION: Setting a enum-like DOM property to a value
> that doesn't represent a valid attribute value
> should throw a TypeError

This affects the setter algorithm for
SVGAnimatedEnumeration
and for SVGPreserveAspectRatio.

Clarifying changes made to:
-  the note regarding reserializing an SVGAnimatedEnumeration,
- the general statement about
silently ignoring invalid values.

Closes #547.

master/changes.html

@@ -284,6 +284,11 @@ <h3 id="types">Basic Data Types and Interfaces chapter</h3>
   <li>Clarify possible UA behavior on getTotalLength, getPointAtLength, getBBox, getCTM, getScreenCTM, isPointInFill
     and isPointInStroke if the current element is a <a>non-rendered element</a>.</li>
   <li>Removed the text-decoration-fill and text-decoration-stroke properties.</li>
+  <li>
+    Setting the DOM property for an enumerated attribute
+    to an out-of-range integer or 0 throws a TypeError.
+    <a href="https://github.com/w3c/svgwg/issues/547">Issue discussion</a>
+  </li>
 </ul>
 </div>
 
@@ -533,6 +538,11 @@ <h3 id="coords">Coordinate Systems, Transformations and Units chapter</h3>
 <div class="changed-since-cr1 cr2 cr3">
   <ul>
     <li>Use DOMMatrix2DInit as parameters for methods</li>
+    <li>
+      Setting the enumerated parts of an <a>SVGPreserveAspectRatio</a> object
+      to an out-of-range integer or 0 throws a TypeError.
+      <a href="https://github.com/w3c/svgwg/issues/547">Issue discussion</a>
+    </li>
   </ul>
 </div>
 

master/coords.html

@@ -3609,7 +3609,7 @@ <h3 id="InterfaceSVGPreserveAspectRatio">Interface SVGPreserveAspectRatio</h3>
   <li>If <var>value</var> is
   <a href="#__svg__SVGPreserveAspectRatio__SVG_PRESERVEASPECTRATIO_UNKNOWN">SVG_PRESERVEASPECTRATIO_UNKNOWN</a>
   or does not have a corresponding entry in the
-  alignment keyword table above, then return.</li>
+  alignment keyword table above, then throw a <a>TypeError</a>.</li>
   <li>Let <var>string</var> be the corresponding keyword
   in the alignment keyword table above for <var>value</var>.</li>
   <li>Append a single U+0020 SPACE character to <var>string</var>.</li>
@@ -3648,7 +3648,7 @@ <h3 id="InterfaceSVGPreserveAspectRatio">Interface SVGPreserveAspectRatio</h3>
   <li>If <var>value</var> is
   <a href="#__svg__SVGPreserveAspectRatio__SVG_MEETORSLICE_UNKNOWN">SVG_MEETORSLICE_UNKNOWN</a>
   or does not have a corresponding entry in the
-  meet-or-slice keyword table above, then return.</li>
+  meet-or-slice keyword table above, then throw a <a>TypeError</a>.</li>
   <li>Let <var>align</var> be the value that would be
   returned from the
   <a href="#__svg__SVGPreserveAspectRatio__align">align</a>

master/definitions.xml

@@ -1228,6 +1228,7 @@
   <term name='NoModificationAllowedError' href='https://heycam.github.io/webidl/#nomodificationallowederror'/>
   <term name='NotSupportedError' href='https://heycam.github.io/webidl/#notsupportederror'/>
   <term name='SyntaxError' href='https://heycam.github.io/webidl/#syntaxerror'/>
+  <term name='TypeError' href='https://heycam.github.io/webidl/#exceptiondef-typeerror'/>
   <term name='CORS settings attribute' href='https://html.spec.whatwg.org/multipage/urls-and-fetching.html#cors-settings-attribute'/>
   <term name='limited to only known values' href='https://html.spec.whatwg.org/multipage/common-dom-interfaces.html#limited-to-only-known-values'/>
   <term name='No CORS' href='https://html.spec.whatwg.org/multipage/urls-and-fetching.html#cors-settings-attribute'/>

master/types.html

@@ -423,7 +423,7 @@ <h3 id="ReflectingAttributes">Reflecting content attributes in the DOM</h3>
 
 <p>
 If the attribute hasn't been specified explicitly in the document markup,
-the reflected object is nonetheless intialized upon access,
+the reflected object is nonetheless initialized upon access,
 to the attribute's inital value.
 If the attribute's initial value is <span class="attr-value">(none)</span>,
 the object is initialized as defined in
@@ -487,8 +487,11 @@ <h3 id="SynchronizingReflectedValues">Synchronizing reflected values</h3>
           value corresponding to <var>number</var>, or the empty string
           if <var>number</var> is 0.
           <p class="note">This means that if the enumeration value is
-          set to the "unknown" value, the content attribute will be
-          set to the empty string.</p></li>
+          somehow set to the "unknown" value, the content attribute will be
+          set to the empty string.
+          However, this unknown value can never be set directly on the <code>SVGAnimatedEnumeration</code> object;
+          it represents an unknown attribute value set in the markup.</p>
+          </li>
           <li>Set the content attribute to <var>keyword</var>.</li>
         </ol>
       </dd>
@@ -665,16 +668,19 @@ <h3 id="InvalidValues">Invalid values</h3>
 <p>If a script sets a <a>reflected</a> DOM attribute
 to an <a>invalid value</a> for the content attribute (e.g.,
 a negative number for an attribute that requires a non-negative
-number or an out-of-range value for an enumeration), unless
+number), unless
 this specification indicates otherwise, no exception shall be
 raised on setting, but the given document fragment shall become
 technically <em>in error</em> as described in
 <a href="conform.html#ErrorProcessing">Error processing</a>.</p>
 
-<p class="issue">
-  Many browsers currently throw errors for out-of-range enumeration values,
-  or explicitly setting an enumeration to the UNKNOWN value.
-  See <a href="https://github.com/w3c/svgwg/issues/547">Should setting an enum IDL to an invalid value throw an error?</a> on GitHub for discussion.
+<p class="note">
+DOM attributes that reflect enumerated values using integer constants are an exception:
+these throw a <a>TypeError</a> when set to an out-of-range integer,
+or to the constant (0) that represents an unknown attribute value.
+This is consistent with the
+<a href="https://heycam.github.io/webidl/#es-enumeration">behavior of the WebIDL enumeration type</a>
+[<a href="refs.html#ref-webidl">WebIDL</a>].
 </p>
 
 
@@ -2201,8 +2207,7 @@ <h3 id="InterfaceSVGAnimatedEnumeration">Interface SVGAnimatedEnumeration</h3>
   <li>Let <var>value</var> be the value being assigned to
   <a href="types.html#__svg__SVGAnimatedEnumeration__baseVal">baseVal</a>.</li>
   <li>If <var>value</var> is 0 or is not the <a>numeric type value</a>
-  for any value of the reflected attribute, then set the reflected
-  attribute to the empty string.</li>
+  for any value of the reflected attribute, then throw a <a>TypeError</a>.</li>
   <li>Otherwise, if the reflecting IDL attribute is
   <a href='painting.html#__svg__SVGMarkerElement__orientType'>orientType</a>
   and <var>value</var> is <a href='painting.html#__svg__SVGMarkerElement__SVG_MARKER_ORIENT_ANGLE'>SVG_MARKER_ORIENT_ANGLE</a>,