[css-fonts-4] [varfont] @font-face descriptors should accept ranges

Incorporate the discussion at w3c#521

Author: litherum

css-fonts-4/Overview.bs

@@ -585,37 +585,43 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 
 	<pre class='descdef mq'>
 	Name: font-style
-	Value: normal | italic | oblique <<angle>> ?
+	Value: normal | italic | oblique [ <<angle>> | <<angle>>-<<angle>> ] ?
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef mq'>
 	Name: font-weight
-	Value: normal | bold | <<number>>
+	Value: normal | bold | [ <<number>> | <<number>>-<<number>> ]
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef mq'>
 	Name: font-stretch
 	Value: normal | ultra-condensed | extra-condensed | condensed | semi-condensed |
-      semi-expanded | expanded | extra-expanded | ultra-expanded | <<percentage>>
+      semi-expanded | expanded | extra-expanded | ultra-expanded | [ <<percentage>> | <<percentage>>-<<percentage>> ]
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	These descriptors define the characteristics of a font face and are
-	used in the process of matching styles to specific faces.  For a font
+	used in the process of matching styles to specific faces. For a font
 	family defined with several <code>@font-face</code> rules, user agents can either
 	download all faces in the family or use these descriptors to selectively
-	download font faces that match actual styles used in document.  The
-	values for these descriptors are the same as those for the corresponding
+	download font faces that match actual styles used in document. The
+	meaning of the values for these descriptors are the same as those for the corresponding
 	font properties except that relative keywords are not allowed, 'bolder' and
-	'lighter'.  If these descriptors are omitted, initial
+	'lighter'. If these descriptors are omitted, initial
 	values are assumed. If specified values are out of range of the accepted values
 	of the property of the same name, the descriptor is treated as a parse error.
 
+	Ranges are accepted in these three descriptors in place of a single value. Where a single
+	value is specified, it has the same meaning as a range with identical startpoint and
+	endpoint. User agents may swap the computed value of the startpoint and endpoint of the range
+	in order to forbid decreasing ranges. Both endpoints are inclusive.
+	The ranges are used in the <a href="#font-matching-algorithm">Font Matching Algorithm</a> below.
+
 	The value for these font face style attributes is used in place of
 	the style implied by the underlying font data.  This allows authors to
 	combine faces in flexible combinations, even in situations where the
@@ -798,10 +804,10 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 		<li>'font-stretch' is tried first. If a font
 		does not have any concept of varying strengths of stretch values, its stretch value
 		is mapped according table in the <a href="#stretchmappings">property definition</a>.
-		If the matching set contains faces with width values
-		matching the 'font-stretch' value, faces with other width
+		If the matching set includes faces with width values
+		containing the 'font-stretch' desired value, faces with other width
 		values are removed from the matching set. If there is no face
-		that exactly matches, a stretch value is chosen using the rules below:
+		which contains the desired value, a stretch value is chosen using the rules below:
 		  <ul>
 		    <li>If the desired stretch value is less than 100, stretch values below the
 		    desired stretch value are checked in descending order followed by
@@ -814,14 +820,14 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 		  </ul>
 		Once the
 		closest matching width has been determined by this process,
-		faces with other widths are removed from the matching set.
+		faces with widths which do not include this determined width are removed from the matching set.
 		</li>
 
 		<li>'font-style' is tried next.
 		If the value of 'font-style' is 'italic', italic faces are
 		checked first, then oblique, then normal faces.  If the value
 		is 'oblique', oblique faces are checked first, then italic
-		faces and then normal faces.  If the value is 'normal',
+		faces and then normal faces. If the value is 'normal',
 		normal faces are checked first, then oblique faces, then
 		italic faces. When checking oblique faces, an oblique angle is chosen using the rules below:
 		<ul>
@@ -833,11 +839,13 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 		    are checked in descending order until 0deg or a negative value is reached.
 		    <li>Otherwise, the same steps as above are performed, substituting negative values for the positive ones above.</li>
 		</ul>
-		During this operation, if a font does not have any concept of varying oblique angles, it is assumed to have an angle of 20deg. Faces with other style values are excluded
-		from the matching set. User agents are permitted to
+		During this operation, if an oblique font does not have any concept of varying oblique angles, it is assumed to have an angle of 20deg.
+		If the search for a normal or italic face successfully determined a font, faces with other style values are excluded
+		from the matching set. Otherwise, if the search for an oblique face successfully determined a font, fonts with oblique angles which do not include
+		this determined angle are excluded from the matching set. User agents are permitted to
 		distinguish between italic and oblique faces within platform
 		font families but this is not required, so all
-		italic or oblique faces may be treated as italic faces. However, within font
+		italic or oblique faces may be treated as italic faces or oblique faces with an angle of 20deg. However, within font
 		families defined via <code>@font-face</code> rules, italic and oblique
 		faces must be distinguished using the value of the
 		'font-style' descriptor.
@@ -853,9 +861,9 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 		If bolder/lighter relative weights are used, the
 		effective weight is calculated based on the inherited weight
 		value, as described in the definition of the 'font-weight'
-		property. Given the desired weight and the weights of faces
+		property. Given the desired weight and the weight ranges of faces
 		in the matching set after the steps above, if the desired
-		weight is available that face matches.  Otherwise, a weight
+		weight is available inside the weight range of a font in the matching set, then that face matches. Otherwise, a weight
 		is chosen using the rules below:
 		  <ul>
 		    <li>If the desired weight is 400, 500 is checked first and then
@@ -872,6 +880,8 @@ at least as dark as its predecessor. Only values between 1 - 999 are valid, and
 		    weights below the desired weight in descending order until a
 		    match is found.</li>
 		  </ul>
+		Once the closest matching weight has been determined by this process,
+		faces with weights which do not include this determined width are removed from the matching set.
 		</li>
 
 		<li>'font-size' must be