[css-fonts-4] Reference syntax spec for parsing comma separated descr…

…iptor see #6340

css-fonts-4/Overview.bs

@@ -1877,23 +1877,11 @@ The <dfn id="at-font-face-rule">''@font-face''</dfn> rule</h3>
 
 <h4 id="font-face-src-parsing">Parsing the 'src!!descriptor' descriptor</h4>
 
-    The value of the 'src!!descriptor' descriptor is parsed piecewise.
 
-    First, opening and closing parentheses are matched.
-    If these parentheses cannot be matched,
-    the value is a parse error.
-    Matching the parentheses has the effect of
-    partitioning the value into multiple regions,
-    each of which is either
-    inside outermost parentheses
-    or outside outermost parentheses.
+	The 'src!!descriptor' descriptor value must be parsed
+	according to section [[css-syntax#parse-comma-separated-list-of-component-values]].
+	Then each component value is parsed according to this grammar:
 
-    Once the value is partitioned,
-    all the commas outside outermost parentheses
-    are located.
-    The value is then split at these comma locations.
-
-    Each item in the split value is then parsed against this grammar:
 
     <pre><<url>> [ format(<<font-format>> [supports <<font-technology>>#]?)]? | local(<<font-face-name>>)</pre>
 
@@ -1903,12 +1891,15 @@ The <dfn id="at-font-face-rule">''@font-face''</dfn> rule</h3>
 
     <pre class="prod"><dfn id="color-font-technology-values">&lt;color-font-technology&gt;</dfn> = [COLRv0 | COLRv1 | SVG | sbix | CBDT ]</pre>
 
-    If parsing a particular item in the split value results in a parse error,
-    that item is thrown out.
-
-    Issue: Define what "thrown out" means
+    If a component value is parsed correctly
+	and is of a format and font technology that the UA supports,
+	add it to the list of supported sources.
+	If parsing a component value results in a parsing error
+	or its format or technology are unsupported,
+	do not add it to the list of supported sources.
 
-    If no item in the split value survives, then the descriptor is a parse error.
+    If there are no supported entries at the end of this process,
+	the value for the 'src!!descriptor' descriptor is a parse error.
 
     These parsing rules allow for graceful fallback of fonts
     for user agents which don't support a particular font technology.