[css-align] Define how justify/align-content affect initial scroll position.

Author: tabatkins

css-align/Overview.bs

@@ -466,11 +466,6 @@ Content Distribution: the 'justify-content' and 'align-content' properties</h2>
 	Animatable: no
 	</pre>
 
-	Issue: This should also affect the initial scroll position.
-	If you align "end", you want to be able to see the "end" stuff when the element first loads,
-	which means the scrollbar has to be scrolled all the way to the end
-	(or equivalent, for scrollable overflows that don't generate scrollbars).
-
 	Aligns the contents of the box as a whole along the box's inline/row/main axis.
 	Values other than <dfn value for="justify-content, align-content">auto</dfn> are <a href="#alignment-values">defined above</a>.
 	If both a <<content-distribution>> and <<content-position>> are given,
@@ -581,6 +576,29 @@ Baseline Content-Alignment</h3>
 	to match its <a>alignment baseline</a> in that axis up to that of its <a>baseline-sharing group</a>.
 	This increases the intrinsic size of the box.
 
+<h3 id="overflow-alignment">
+Overflow and Alignment: scroll positions</h3>
+
+	The <a>content distribution properties</a> also affect the initial scroll position,
+	setting it to display the appropriate portion of the scrollable area.
+	In other words,
+	the scrollable area is aligned relative to the viewport
+	as specified by the <a>content distribution property</a>.
+
+	<div class='example'>
+		For example,
+		if a scrollable flex container is set to ''justify-content: flex-end;''
+		or ''justify-content: flex-start;'' with a 'flex-direction' of ''row-reverse'',
+		it will be initially displayed scrolled all the way to the main-end edge of the scrollable area,
+		and its content will overflow its main-start edge.
+	</div>
+
+	Issue: This section is under discussion in the WG.
+
+	Issue: This needs to be integrated with overflow-anchor, when the property exists,
+	so that you get the same behavior whether an elements *starts out* overflowing,
+	or is filled element-by-element.
+
 <h2 id='self-alignment'>
 Self-Alignment: Aligning the Box within its Parent</h2>