[css-scroll-snap-1] Add bottom-snapped console example from http://tabatkins.github.io/specs/css-sticky-scrollbars/#intro #4371

Author: fantasai

css-scroll-snap-1/Overview.bs

@@ -396,6 +396,9 @@ Scroll Snap Strictness: the ''scroll-snap-type/none'', ''proximity'', and ''mand
     Otherwise, the box has no <a>scroll snap container</a>,
     and its <a>snap positions</a> do not trigger <a>snapping</a>.
 
+<h4 id="re-snap">
+Re-snapping After Layout Changes</h4>
+
     If the content or layout of the document changes
     (e.g. content is added, moved, deleted, resized)
     such that the content of a <a>snapport</a> changes,
@@ -407,6 +410,39 @@ Scroll Snap Strictness: the ''scroll-snap-type/none'', ''proximity'', and ''mand
     the scroll container must be re-snapped to that same snap position
     after the content change.
 
+	<div class="example">
+		In the following example,
+		the log console,
+		when initially loaded and as each message is added to the bottom,
+		remains snapped to the bottom of the content
+		unless the user has scrolled away from that edge:
+
+		<pre class="lang-css">
+			.log {
+			  scroll-snap-type: proximity;
+			  align-content: end;
+			}
+			.log::after {
+			  display: block;
+			  content: "";
+			  scroll-snap-align: end;
+			}
+		</pre>
+
+		The rules create a single [=scroll snap area=]
+		represented by the ''::after'' pseudo-element,
+		positioned at the very bottom of a [=scroll snap container=].
+		If the user scrolls “near” the bottom,
+		the container will snap to it.
+		If more content is dynamically added to the container,
+		it’ll remain snapped to it
+		(because scroll containers are required
+		to re-snap to the same scroll snap area
+		if it still exists after any changes).
+		However, if the user has scrolled to somewhere else in the logs,
+		it won’t do anything at all.
+	</div>
+
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