[css-overflow] Enable clamping by line and height at the same time (w3c#12772)

See w3c#12041

Co-authored-by: Andreu Botella <andreu@andreubotella.com>

Author: frivoal

css-overflow-4/Overview.bs

@@ -973,14 +973,14 @@ Forcing a Break After a Set Number of Lines: the 'max-lines' property</h3>
 		If fewer than <var>N</var> line boxes exist,
 		then 'max-lines' introduces no <a>region break</a>.
 	- If the box is a [=line-clamp container=],
-		its [=clamp point=] is set
+		its [=line-based clamp point=] is set
 		to the first possible clamp point after
 		its <var>N</var>th
 		descendant <a>in-flow</a> <a>line box</a>.
 		If fewer than <var>N</var> line boxes exist,
 		or if there are no possible clamp points
 		after the <var>N</var>th descendant <a>in-flow</a> <a>line box</a>,
-		then that line-clamp container has no clamp point.
+		then that line-clamp container has no [=line-based clamp point=].
 
 
 	Only line boxes in the same <a>block formatting context</a>
@@ -1196,17 +1196,21 @@ Fragmentation of Overflow: the 'continue' property</h3>
 	- A point between two [=in-flow=] [=block-level=] sibling boxes
 		in the line-clamp container's [=block formatting context=].
 
-	If the [=line-clamp container=]'s [=block formatting context root=]
-	has a [=computed value=] of 'max-lines' other than ''max-lines/none'',
-	then that property will determine the [=clamp point=].
-	Otherwise, the clamp point will be set to the last possible clamp point
+	The <dfn>auto clamp point</dfn> will be set to the last possible clamp point
 	such that, for it and all previous possible clamp points,
 	the line-clamp container's [=automatic block size=]
 	(as determined below)
 	is not greater than the [=block size=] the box would have
 	if its automatic block size were infinite.
 	If the [=block size=] would be infinite,
-	then there is no clamp point.
+	then there is no [=auto clamp point=].
+	Additionally,
+	when the [=line-clamp container=]'s [=block formatting context root=]
+	has a [=computed value=] of 'max-lines' other than ''max-lines/none'',
+	then that property determines the <dfn>line-based clamp point</dfn>.
+	The actual [=clamp point=] used is
+	either the [=auto clamp point=] or the [=line-based clamp point=],
+	choosing the earlier when both exist.
 
 	Within a [=line-clamp container=],
 	the following boxes and line boxes become [=invisible boxes=]: