add start of polygon vertex rounding

Author: astearns

css-shapes-1/Overview.bs

@@ -20,6 +20,7 @@ Abstract: CSS Shapes describe geometric shapes for use in CSS. For Level 1, CSS
 <pre class='link-defaults'>
 spec:css2; type:property; text:margin
 spec:css-backgrounds-3; type:property; text:border-radius
+spec:css-inline; type:dfn; text:initial letter box
 spec:css-masking-1; type: value
 	text: nonzero
 	text: evenodd
@@ -352,7 +353,8 @@ Supported Shapes</h3>
 		)
 
 		<<polygon()>> = polygon(
-			<<'fill-rule'>>? ,
+			<<'fill-rule'>>? 
+			[ round <<length>> ]? ,
 			[<<length-percentage>> <<length-percentage>>]#
 		)
 
@@ -461,7 +463,7 @@ Supported Shapes</h3>
 			* The <<radial-size>> argument defines
 				the circle's radius.
 				Rather than referring to the [=gradient box=],
-				values are resolved against the [=<basic-shape>/reference box=].
+				values are resolved against the [=reference box=].
 
 			* Two <<length-percentage>> values are invalid.
 
@@ -475,7 +477,7 @@ Supported Shapes</h3>
 			* The <<radial-size>> argument defines
 				the horizontal and vertical radiuses of the ellipse.
 				Rather than referring to the [=gradient box=],
-				values are resolved against the [=<basic-shape>/reference box=].
+				values are resolved against the [=reference box=].
 
 			* The <<position>> argument defines
 				the center of the ellipse.
@@ -488,10 +490,29 @@ Supported Shapes</h3>
 				to determine the interior
 				Defaults to ''nonzero'' if omitted.
 
+			* An optional <<length>> after a <css>round</css> keyword 
+				defines rounding for each vertex of the polygon.
+				The length is the radius of a circle 
+				whose center lies on the bisector 
+				of the smaller angle of the vertex,
+				and that is tangential 
+				to both sides of the vertex.
+
+				To avoid rounding more
+				than half of any line segment,
+				the rounding of each vertex 
+				must be clamped separately 
+				such that the radius is never more than 
+				the smaller of <code>tan(angle/2) segment / 2</code> 
+				evaluated against both vertex line segments.
+
+
+			Note: vertex rounding needs examples and tests.
+
 			* Each <<length-percentage>> pair
 				specifies a vertex of the polygon,
 				as a horizontal and vertical offset
-				from the left and top edges of the [=<basic-shape>/reference box=].
+				from the left and top edges of the [=reference box=].
 
 			The UA must close a polygon
 			by connecting the last vertex
@@ -1129,7 +1150,7 @@ Change Log</h2>
 	Since <a href="https://www.w3.org/TR/2022/CRD-css-shapes-1-20221115/">15 November 2022</a></h3>
 
 	<ul>
-		<li></li>
+		<li>Added vertex rounding for polygon() for <a href="https://github.com/w3c/csswg-drafts/issues/9843">issue #9843</a> </li>
 	</ul>
 
 <h3 class="no-num" id="20140320">