[css-fonts-4] Fix #514 italic not a fallback for oblique

Author: svgeesus

css-fonts-4/Overview.bs

@@ -740,7 +740,10 @@ Font style: the 'font-style!!property' property</h3>
             but the mapping within the font is disregarded.)
             Fractional and negative values are accepted; however,
             values less than -90deg or values greater than 90deg are <a>invalid</a>.
-            If no oblique faces exist, this value can match an italic face.
+			If no oblique faces exist,
+			<!-- https://github.com/w3c/csswg-drafts/issues/514#issuecomment-402010784 -->
+			and 'font-synthesis-style' has the value auto,
+			a synthetic oblique face will be generated.
     </dl>
 
     A font family might contain no italic or oblique faces,
@@ -766,9 +769,6 @@ Font style: the 'font-style!!property' property</h3>
 	when using variations
 	to produce oblique faces.
 
-    ISSUE: The threshold for preferring oblique over normal
-    <a href="https://github.com/w3c/csswg-drafts/issues/2295">should be lower than the average angle</a>.
-
     Issue: What direction should positive and negative obliques skew in vertical writing mode?
     How do we achieve skews in the opposite dimension
     (needed for vertical writing)?
@@ -3066,10 +3066,17 @@ if all font style properties were set to their initial value.
 						faces with oblique values which do not include the desired oblique value are removed from the matching set.
 					2. Otherwise, oblique values above the desired oblique value are checked in ascending order followed by
 						oblique values below the desired oblique value, until 0 is hit. Only positive values of oblique values are checked in this stage.
-					3. If no match is found, italic values greater than or equal to 1 are checked in ascending order
+					3. If 'font-synthesis-style' has the value 'font-synthesis-style/auto',
+					then for variable fonts with a slnt axis
+					a match is is created by setting the slnt value
+					with the specified oblique value;
+					otherwise,
+					a fallback match is produced
+					by geometric shearing to the specified oblique value.
+					4. If no match is found, italic values greater than or equal to 1 are checked in ascending order
 						followed by italic values below 1 in descending order, until 0 is hit. Only positive values of italic values are checked in this stage.
-					4. If no match is found, oblique values less than or equal to 0deg are checked in descending order until a match is found.
-					5. If no match is found, italic values less than or equal to 0 are checked in descending order until a match is found.
+					5. If no match is found, oblique values less than or equal to 0deg are checked in descending order until a match is found.
+					6. If no match is found, italic values less than or equal to 0 are checked in descending order until a match is found.
 
 						<div class="example">
 							Similar to the <a href="#ascendingstretch">previous example</a>, here is the conceptual distance graph for an element styled with "font-style: oblique 40deg":
@@ -3089,11 +3096,18 @@ if all font style properties were set to their initial value.
 					2. Otherwise, oblique values below the desired oblique value are checked in descending order until 0 is hit, followed by
 						oblique values above the desired oblique value. Only positive values of oblique values are checked
 						in this stage.
-					3. If no match is found, italic values less than 1 are checked in descending order until 0 is hit,
+					3. If 'font-synthesis-style' has the value 'font-synthesis-style/auto',
+					then for variable fonts with a slnt axis
+					a match is is created by setting the slnt value
+					with the specified oblique value;
+					otherwise,
+					a fallback match is produced
+					by geometric shearing to the specified oblique value.
+					4. If no match is found, italic values less than 1 are checked in descending order until 0 is hit,
 						followed by italic values above 1 in ascending order. Only positive values of italic values
 						are checked in this stage.
-					4. If no match is found, oblique values less than or equal to 0deg are checked in descending order until a match is found.
-					5. If no match is found, italic values less than or equal to 0 are checked in descending order until a match is found.
+					5. If no match is found, oblique values less than or equal to 0deg are checked in descending order until a match is found.
+					6. If no match is found, italic values less than or equal to 0 are checked in descending order until a match is found.
 
 					<div class="example">
 						Similar to the <a href="#ascendingstretch">previous example</a>, here is the conceptual distance graph for an element styled with "font-style: oblique 13deg":