[css-snappoints] Adding definition for scroll snap area and tweaking …

…so bikeshed will build.

css-snappoints/Overview.src.html

@@ -12,7 +12,7 @@ <h1>CSS Scroll Snap Points Module Level 1</h1>
 Editor: Jacob Rossi, Microsoft
 Abstract: This module contains features to control panning and scrolling behavior with "snap points".
 !Issue Tracking: <a href="http://wiki.csswg.org/spec/css-snappoints">http://wiki.csswg.org/spec/css-snappoints</a>
-Ignored Terms: scroll-snap-points-*
+Ignored Terms: scroll-snap-points-*, containing block chain
 </pre>
 
 <h2 id="intro">Introduction</h2>
@@ -191,7 +191,11 @@ <h2 id="definitions">Definitions</h2>
         <dd>
             A scroll container's snap alignment container is the rectangle obtained by reducing its visual viewport by its 'scroll-snap-padding'.
 
-        <dt><dfn export>snap position</dfn>
+        <dt><dfn lt="scroll snap area" local-lt="snap area" export>snap area</dfn>
+        <dd>
+            An element's snap area is the rectangle obtained by expanding its specified box by its 'scroll-snap-area'.
+
+        <dt><dfn lt="scroll snap position" local-lt="snap position" export>snap position</dfn>
         <dd>
             For a scroll container, a particular value for its scroll offset is a snap position if when scrolled to that offset the visual viewport of the scroll container would align with a descendent element in the manner specified by the scroll snap properties.
     </dl>