[cssom-1] Add updating flag to CSS declaration block to avoid serialize-and-reparse on style attribute.

Author: upsuper

cssom-1/Overview.bs

@@ -1952,6 +1952,10 @@ the DOM a <a>CSS declaration block</a> is a
  <dt><dfn>owner node</dfn>
  <dd>The {{Element}} that the <a>CSS declaration block</a> is associated with, if any, or
  null otherwise.
+
+ <dt><dfn>updating flag</dfn>
+ <dd>Unset by default. Set when the <a>CSS declaration block</a> is updating
+ the <a for="CSSStyleDeclaration">owner node</a>'s <code>style</code> attribute.
 </dl>
 
 To <dfn>parse a CSS declaration block</dfn> from a string <var>string</var>, follow these steps:
@@ -2038,6 +2042,7 @@ A <a>CSS declaration block</a> has these <a>attribute change steps</a> for its <
 
 <ol>
  <li>If the <a for="CSSStyleDeclaration">readonly flag</a> is set, terminate these steps.
+ <li>If the <a for="CSSStyleDeclaration">updating flag</a> is set, terminate these steps.
  <li>If <var>localName</var> is not "<code>style</code>", or <var>namespace</var> is not null, terminate these steps.
  <li>If <var>value</var> is null, empty the <a for="CSSStyleDeclaration">declarations</a>.
  <li>Otherwise, let the <a for="CSSStyleDeclaration">declarations</a> be the result of <a>parse a CSS declaration block</a>
@@ -2055,6 +2060,18 @@ When a <a>CSS declaration block</a> object is created, then:
  <a>parse a CSS declaration block</a> from a string <var>value</var>.
 </ol>
 
+To <dfn>update style attribute for</dfn> <var>declaration block</var> means to run the steps below:
+
+<ol>
+ <li>Assert: <var>declaration block</var>'s <a for="CSSStyleDeclaration">readonly flag</a> is unset.
+ <li>Let <var>owner node</var> be <var>declaration block</var>'s <a for="CSSStyleDeclaration">owner node</a>.
+ <li>If <var>owner node</var> is null, terminate these steps.
+ <li>Set <var>declaration block</var>'s <a for="CSSStyleDeclaration">updating flag</a>.
+ <li><a>Set an attribute value</a> for <var>owner node</var> using "<code>style</code>" and the result of
+ <a lt="serialize a CSS declaration block">serializing</a> <var>declaration block</var>.
+ <li>Unset <var>declaration block</var>'s <a for="CSSStyleDeclaration">updating flag</a>.
+</ol>
+
 The <dfn id=concept-shorthands-preferred-order>preferred order</dfn> of a list of shorthand properties <var>shorthands</var> is as follows:
 
 <ol>
@@ -2100,8 +2117,7 @@ Setting the {{CSSStyleDeclaration/cssText}} attribute must run these steps:
  <li>Empty the <a for="CSSStyleDeclaration">declarations</a>.
  <li><a lt="Parse a CSS declaration block">Parse</a> the given value and, if the return value is not the empty list, insert the items in the list
  into the <a for="CSSStyleDeclaration">declarations</a>, in <a>specified order</a>.
- <li>If the <a for="CSSStyleDeclaration">owner node</a> is not null, <a>set an attribute value</a> for <a for="CSSStyleDeclaration">owner node</a>
- using "<code>style</code>" and the result of <a lt="serialize a CSS declaration block">serializing</a> the <a for="CSSStyleDeclaration">declarations</a>.
+ <li><a>Update style attribute for</a> the <a>CSS declaration block</a>.
 </ol>
 
 The <dfn attribute for=CSSStyleDeclaration>length</dfn> attribute must return the number of <a lt="CSS declaration">CSS
@@ -2187,8 +2203,7 @@ The <dfn method for=CSSStyleDeclaration>setProperty(<var>property</var>, <var>va
  <li>Otherwise, <a lt="set a CSS declaration">set the CSS declaration</a> <var>property</var> with value <var>component value list</var>, with
  the <i>important</i> flag set if <var>priority</var> is not the empty string, and unset otherwise, and with the list of declarations being the
  <a for="CSSStyleDeclaration">declarations</a>.
- <li>If the <a for="CSSStyleDeclaration">owner node</a> is not null, <a>set an attribute value</a> for <a for="CSSStyleDeclaration">owner node</a>
- using "<code>style</code>" and the result of <a lt="serialize a CSS declaration block">serializing</a> the <a for="CSSStyleDeclaration">declarations</a>.
+ <li><a>Update style attribute for</a> the <a>CSS declaration block</a>.
 </ol>
 
 To <dfn>set a CSS declaration</dfn> <var>property</var> with a value <var>component value list</var> and optionally with an <i>important</i> flag set, in
@@ -2227,8 +2242,7 @@ steps:
  value list</var>, and with the list of declarations being the <a for="CSSStyleDeclaration">declarations</a>.
  <li>Otherwise, <a lt="set a CSS declaration value">set the CSS declaration value</a> <var>property</var> to the value <var>component value
  list</var>, and with the list of declarations being the <a for="CSSStyleDeclaration">declarations</a>.
- <li>If the <a for="CSSStyleDeclaration">owner node</a> is not null, <a>set an attribute value</a> for <a for="CSSStyleDeclaration">owner node</a>
- using "<code>style</code>" and the result of <a lt="serialize a CSS declaration block">serializing</a> the <a for="CSSStyleDeclaration">declarations</a>.
+ <li><a>Update style attribute for</a> the <a>CSS declaration block</a>.
 </ol>
 
 To <dfn>set a CSS declaration value</dfn> to a value <var>component value list</var> in a list of declarations <var>declarations</var>, follow these steps:
@@ -2261,8 +2275,7 @@ these steps:
  <li>Otherwise, <a lt="set a CSS declaration priority">set the CSS declaration priority</a> <var>property</var> with the <i>important</i> flag set
  if <var>priority</var> is not the empty string, and unset otherwise, and with the list of declarations being the
  <a for="CSSStyleDeclaration">declarations</a>.
- <li>If the <a for="CSSStyleDeclaration">owner node</a> is not null, <a>set an attribute value</a> for <a for="CSSStyleDeclaration">owner node</a>
- using "<code>style</code>" and the result of <a lt="serialize a CSS declaration block">serializing</a> the <a for="CSSStyleDeclaration">declarations</a>.
+ <li><a>Update style attribute for</a> the <a>CSS declaration block</a>.
 </ol>
 
 To <dfn>set a CSS declaration priority</dfn> <var>property</var> optionally with an <i>important</i> flag set, in a list of declarations
@@ -2294,9 +2307,7 @@ The <dfn method for=CSSStyleDeclaration>removeProperty(<var>property</var>)</dfn
  <li>Otherwise, if <var>property</var> is a <a>case-sensitive</a> match for a
  <a for="CSS declaration">property name</a> of a <a>CSS declaration</a> in the
  <a for="CSSStyleDeclaration">declarations</a>, remove that <a>CSS declaration</a> and let <var>removed</var> be true.
- <li>If <var>removed</var> is true and <a for="CSSStyleDeclaration">owner node</a> is not null, <a>set an attribute value</a>
- for <a for="CSSStyleDeclaration">owner node</a> using "<code>style</code>" and the result of
- <a lt="serialize a CSS declaration block">serializing</a> the <a for="CSSStyleDeclaration">declarations</a>.
+ <li>If <var>removed</var> is true, <a>Update style attribute for</a> the <a>CSS declaration block</a>.
  <li>Return <var>value</var>.
 </ol>