[css-snappoints] Adding trapping behavior, deleting duplicate definitions so bikeshed will generate again and updating generated html.

Author: ChumpChief

css-snappoints/Overview.bs

@@ -216,16 +216,6 @@ Definitions {#definitions}
         <dd>
             An element which provides a scrolling user interface as described in [[!CSS21]], particularly in the section on overflow.
 
-        <dt><dfn export>snapport</dfn>
-        <dd>
-            A scroll container's snapport is the rectangle obtained by reducing its scrollport by its 'scroll-snap-padding'.
-
-            Issue: Better name for this concept?
-
-        <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 border box by its 'scroll-snap-margin'.
-
         <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 scrollport of the scroll container would align with a descendent element in the manner specified by the scroll snap properties.
@@ -267,7 +257,7 @@ Scroll Snapping Rules: the 'scroll-snap-type' property {#scroll-snap-type}
     Animatable: no
     </pre>
 
-    The 'scroll-snap-type' property specifies how strictly a <a>scroll container</a> should <a>snap</a>, and which axes are considered.
+    The 'scroll-snap-type' property specifies whether a <a>scroll container</a> is a <a>scroll snap container</a>, how strictly a <a>scroll container</a> should <a>snap</a>, and which axes are considered.
 
     The <dfn noexport lt="strictness value">strictness values</dfn>
     (''scroll-snap-type/none'', ''proximity'', ''mandatory'')
@@ -283,21 +273,39 @@ Scroll Snapping Rules: the 'scroll-snap-type' property {#scroll-snap-type}
     <dl dfn-type="value" dfn-for="scroll-snap-type">
         <dt><dfn>none</dfn>
         <dd>
-            The <a>scroll container</a> must not <a>snap</a>.
+            If specified on a <a>scroll container</a>, the <a>scroll container</a> must not <a>snap</a>.
 
         <dt><dfn>mandatory</dfn>
         <dd>
-            The <a>scroll container</a> is required to be <a>snapped</a> to a snap position when there are no active scrolling operations.  If a reachable snap position exists then the scroll container must <a>snap</a> at the termination of a scroll.  If no reachable snap position exists then no <a>snapping</a> occurs.
+            If specified on a <a>scroll container</a>, the <a>scroll container</a> is required to be <a>snapped</a> to a snap position when there are no active scrolling operations.  If a reachable snap position exists then the scroll container must <a>snap</a> at the termination of a scroll.  If no reachable snap position exists then no <a>snapping</a> occurs.
 
             If the content changes such that the scroll container would no longer be <a>snapped</a> (e.g. content is added, moved, deleted, resized) to the same snap position it was snapped to before the content change, the scroll container must be re-snapped.  If the same snap position it was snapped to before the content change still exists (e.g. its associated element was not deleted) and is reachable, the scroll container must be re-snapped to that same snap position after the content change.
 
+            If specified on a non-<a>scroll container</a>,
+            this value “traps” descendant boxes’ <a>snap positions</a>,
+            preventing them from affecting any ancestor <a>scroll containers</a>.
+
         <dt><dfn>proximity</dfn>
         <dd>
-            The <a>scroll container</a> may <a>snap</a> to a snap position at the termination of a scroll, at the discretion of the UA given the parameters of the scroll.
+            If specified on a <a>scroll container</a>, the <a>scroll container</a> may <a>snap</a> to a snap position at the termination of a scroll, at the discretion of the UA given the parameters of the scroll.
 
             If the content changes such that the scroll container would no longer be <a>snapped</a> (e.g. content is added, moved, deleted, resized) to the same snap position it was snapped to before the content change and that same snap position still exists (e.g. its associated element was not deleted) and is reachable, the scroll container must be re-snapped to that same snap position after the content change.
+
+            If specified on a non-<a>scroll container</a>,
+            this value “traps” descendant boxes’ <a>snap positions</a>,
+            preventing them from affecting any ancestor <a>scroll containers</a>.
     </dl>
 
+    A box <dfn export>captures snap positions</dfn>
+    if it is a <a>scroll container</a>
+    <em>or</em> has a value other than ''scroll-snap-type/none'' for 'scroll-snap-type'.
+    If a box's nearest <a lt="captures snap positions">snap-position capturing</a> ancestor
+    on its <a>containing block chain</a>
+    is a <a>scroll container</a> with a non-''scroll-snap-type/none'' value for 'scroll-snap-type',
+    that is the box's <dfn export local-lt="snap container">scroll snap container</dfn>.
+    Otherwise, the box has no <a>scroll snap container</a>,
+    and its <a>snap positions</a> do not trigger <a>snapping</a>.
+
     The <dfn noexport lt="axis value">axis values</dfn>
     specify what axis(es) are affected by <a>snap positions</a>,
     and whether <a>snap positions</a> are evaluated independently per axis,
@@ -338,7 +346,7 @@ Scroll Snapping Rules: the 'scroll-snap-type' property {#scroll-snap-type}
     Authors should use mandatory snap positions with consideration of
     varyingly-sized screens and (if applicable) varying-sized content.
     In particular, although access to snapped elements larger than the viewport
-    is <a href="#snap-overflow">handled by the UA</a>,
+    is handled by the UA,
     if authors assign mandatory snapping to non-adjacent siblings,
     content in between can become inaccessible
     in cases where it is longer than the screen.