[css-overflow-3] Fill out max-lines section.

Author: fantasai

css-overflow-3/Overview.bs

@@ -17,7 +17,8 @@ Abstract: This module contains the features of CSS relating to scrollable overfl
 !Change Log: <a href="https://hg.csswg.org/drafts/log/tip/css-overflow/Overview.src.html">from 28 March 2013 to 27 January 2015</a>
 !Change Log: <a href="https://hg.csswg.org/drafts/log/tip/css3-overflow/Overview.src.html">from 31 July 2012 to 27 March 2013</a>
 Ignored Vars: B, P
-Ignored Terms: padding edge
+Ignored Terms: padding edge, viewport, line box, flex order
+At Risk: the 'max-lines' property
 Status Text: <strong>This update trims away most of the experimental new ideas
    for handling overflow that were described in the <a href="https://www.w3.org/TR/2013/WD-css-overflow-3-20130418/">previous Working Draft</a>.
    These ideas are not abandoned; they are merely <a href="https://drafts.csswg.org/css-overflow/">deferred until Level 4</a>.</strong>
@@ -30,9 +31,9 @@ Status Text: <strong>This update trims away most of the experimental new ideas
 <!-- - Abstract has the most introductory sentence last -->
 <!-- FIXME: other bikeshed issues -->
 <pre class="link-defaults">
-spec:css-transforms-1; type:property; text:transform-style
+spec:css-transforms-2; type:property; text:transform-style
 type: dfn; spec:css-multicol-1; text:overflow column
-type: dfn; spec:css-transforms-1; text:3d rendering context
+type: dfn; spec:css-transforms-2; text:3d rendering context
 </pre>
 <!-- FIXME: the break-* link doesn't actually work! -->
 <pre class="anchors">
@@ -432,21 +433,67 @@ Scrolling Origin, Direction, and Restriction</h3>
 <h2 id="max-lines">
 Limiting Number of Visible Text Lines: the 'max-lines' property</h2>
 
-
 	<pre class=propdef>
 		Name: max-lines
 		Value: none | <<integer>>
 		Initial: none
-		Applies to: all non-inline elements
+		Applies to: <a>block containers</a> (excluding <a>multi-column containers</a>)
 		Inherited: no
 		Animatable: as integer
 		Percentages: N/A
 		Media: visual
 		Computed value: specified value
 	</pre>
 
-	Issue: Add back 'max-lines', so we can kill the unspecified WebKit feature that does this poorly.
+	This property allows limiting the contents of a block container
+	to the specified number of lines;
+	remaining content is fragmented away
+	and neither rendered nor measured.
+	Specifically,
 
+	<ul>
+		<li>The box becomes a <a>fragmentation container</a>
+			that captures <a>region breaks</a>.
+
+		<li>A <a>region break</a> [[!CSS-BREAK-3]]
+			is forced after its <var>N</var>th
+			descendant <a>in-flow</a> <a>line box</a>,
+			where <var>N</var> is the specified value of 'max-lines'.
+			For this purpose,
+			line boxes are counted in
+			<span class="issue"><a>document order</a> OR
+			visual order
+			(<a>grid order</a> in <a>grid containers</a>,
+			<a>flex order</a> in <a>flex containers</a>,
+			and <a>document order</a> in all other <a>display types</a>)</span>.
+
+			If fewer than <var>N</var> line boxes exist,
+			then 'max-lines' introduces no <a>region break</a>.
+
+		<li>The position of the first forced <a>region break</a>
+			(whether imposed by 'max-lines' or by another mechanism,
+			such as the 'break-before'/'break-after' properties)
+			is treated as the end of the <a>fragmentation container</a>,
+			and the rest of the <a>fragmented flow</a> is discarded,
+			as if it were ''display: none'':
+			it is neither rendered,
+			nor measured as part of the box’s contents for the purpose of
+			finding its <a lt="min-content size">min-content</a> and <a>max-content sizes</a>,
+			nor does allow user interaction.
+
+			Note: In the case of <a href="https://www.w3.org/TR/css-break-3/#parallel-flows">parallel fragmentation flows</a>,
+			content occuring after the <a>fragmentation break</a> in the box tree
+			could still be rendered,
+			if it is laid out above the position
+			representing the end of this <a>fragmentation container</a>.
+
+			<!-- Honoring forced breaks from other sources
+			is to handle future use cases,
+			such as using 'max-lines' to size the first region
+			in a two-region section,
+			where the first region is for styling the first N lines of the article
+			differently from the rest. -->
+	</ul>
 
 <h2 id="static-media">
 Overflow in static media</h2>