[css-overflow-3] Remove allowance for worse behavior

Instead, add note that legacy -webkit- implementations may be wacky.

See w3c#2905

Author: frivoal

css-overflow-3/Overview.bs

@@ -873,17 +873,6 @@ Indicating Block-Axis Overflow: the 'block-ellipsis' property</h3>
 	The [=block overflow ellipsis=] must not be included
 	in either the ''::first-letter'' nor the ''::first-line'' pseudo-elements.
 
-	If there is no next <a>fragmentation container</a>
-	and thus the remainder of the content after the break would be discarded,
-	then the UA may instead visually replace the contents of the line,
-	as it does for 'text-overflow'.
-
-	Note: Allowing the UA to visually replace the content of the line as with 'text-overflow'
-	is allowed as an implementation convenience,
-	to avoid blocking the whole feature on a comparatively small detail.
-	However, that behavior is less desirable,
-	and may be removed in later levels of this specification.
-
 	If there is a subsequent <a>fragmentation container</a> in the [=fragmentation context=]
 	that would receive subsequent content,
 	then the content displaced by the <a>block overflow ellipsis</a>
@@ -1023,6 +1012,17 @@ Legacy compatibility</h4>
 	and the computed value of the '-webkit-box-orient' property on the parent
 	is ''-webkit-box-orient/vertical''.
 
+	Note: Implementations of the legacy '-webkit-line-clamp' property
+	have not behaved identically to what is specified here.
+	The historical behavior is quirky and less robust,
+	as documented for example in <a href="https://medium.com/mofed/css-line-clamp-the-good-the-bad-and-the-straight-up-broken-865413f16e5">this blog post</a>.
+	The current design learns from the mistakes of that early experiment,
+	and is intended to be sufficiently compatible with existing content
+	that implementations can eventually be changed to follow to the specified behavior.
+	If further adjustments are found to be necessary,
+	they will be incorporated to this specification.
+	In the meanwhile, authors should be aware that there may be discrepancies.
+
 <h3 id="max-lines">
 Forcing a Break After a Set Number of Lines: the 'max-lines' property</h3>