[css-variables] Better define that <fallback> can contain commas.

--HG--
extra : rebase_source : 01b802db256ae5479c8b4548d972ba763408b77f

Author: tabatkins

css-variables/Overview.html

@@ -398,7 +398,7 @@ <h2 id="using-variables" data-level="3"><span class="secno">3 </span>
 	which can then be substituted into another property with the <a data-autolink="maybe" class="css">var()</a> function.
 	The syntax of <a data-autolink="maybe" class="css">var()</a> is:
 
-	</p><pre><dfn id="default-var-type">&lt;variable&gt;</dfn> = var( <var>variable-name</var> [, <var>&lt;fallback&gt;</var> ]? )
+	</p><pre><dfn id="default-var-type">&lt;variable&gt;</dfn> = var( <var>variable-name</var> [, <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a> ]? )
 </pre>
 <p>	A variable can be used in place of any part of a value in any property on an element.
 	Variables can not be used as
@@ -408,13 +408,21 @@ <h2 id="using-variables" data-level="3"><span class="secno">3 </span>
 	(Doing so usually produces invalid syntax,
 	or else a value whose meaning has no connection to the variable.)
 
-</p><p>	The <var>&lt;fallback&gt;</var> value is identical to the syntax of a <a data-autolink="link" href="#custom-property">custom property</a> value.
+</p><p>	The <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a> value is identical to the syntax of a <a data-autolink="link" href="#custom-property">custom property</a> value:
+	it accepts anything allowed by the core syntax of CSS
+	(except that, since it's a value in a function rather than a value in a declaration,
+	some tokens that were allowed in a <a data-autolink="link" href="#custom-property">custom property</a> don't work in a <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a> and vice versa,
+	because they'd close the function early).
+
+</p><p class="note">	Note: The syntax of <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a>, like that of <a data-autolink="link" href="#custom-property">custom properties</a>, allows commas.
+	For example, a variable use like <a data-autolink="maybe" class="css">var(foo, red, blue)</a> defines a fallback of <a data-autolink="maybe" class="css">red, blue</a>;
+	that is, anything between the first comma and the end of the function is considered a <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a> value.
 
 </p><p>	If the variable named by the first argument is valid, 
 	the variable's value is substituted as normal. 
 	If the variable is invalid, 
-	and a <var>&lt;fallback&gt;</var> was provided, 
-	the <var>&lt;fallback&gt;</var> is substituted instead. 
+	and a <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a> was provided, 
+	the <a data-autolink="link" class="production"><var>&lt;fallback&gt;</var></a> is substituted instead. 
 	Otherwise, the result of evaluating the <a data-autolink="maybe" class="css">var()</a> function will mean 
 	that the containing declaration is invalid at computed-value time.
 

css-variables/Overview.src.html

@@ -340,7 +340,7 @@ <h2 id='using-variables'>
 	The syntax of ''var()'' is:
 
 	<pre>
-	<dfn id='default-var-type'>&lt;variable></dfn> = var( <var>variable-name</var> [, <var>&lt;fallback></var> ]? )
+	<dfn id='default-var-type'>&lt;variable></dfn> = var( <var>variable-name</var> [, <<fallback>> ]? )
 	</pre>
 
 	A variable can be used in place of any part of a value in any property on an element.
@@ -351,13 +351,21 @@ <h2 id='using-variables'>
 	(Doing so usually produces invalid syntax,
 	or else a value whose meaning has no connection to the variable.)
 
-	The <var>&lt;fallback></var> value is identical to the syntax of a <a>custom property</a> value.
+	The <<fallback>> value is identical to the syntax of a <a>custom property</a> value:
+	it accepts anything allowed by the core syntax of CSS
+	(except that, since it's a value in a function rather than a value in a declaration,
+	some tokens that were allowed in a <a>custom property</a> don't work in a <<fallback>> and vice versa,
+	because they'd close the function early).
+
+	Note: The syntax of <<fallback>>, like that of <a>custom properties</a>, allows commas.
+	For example, a variable use like ''var(foo, red, blue)'' defines a fallback of ''red, blue'';
+	that is, anything between the first comma and the end of the function is considered a <<fallback>> value.
 
 	If the variable named by the first argument is valid, 
 	the variable's value is substituted as normal. 
 	If the variable is invalid, 
-	and a <var>&lt;fallback></var> was provided, 
-	the <var>&lt;fallback></var> is substituted instead. 
+	and a <<fallback>> was provided, 
+	the <<fallback>> is substituted instead. 
 	Otherwise, the result of evaluating the ''var()'' function will mean 
 	that the containing declaration is invalid at computed-value time.