[css-overscroll-1] Never mind, exclude single-axis scrollers from the scroll chain in their non-scrolling axis.

Author: tabatkins

css-overscroll-1/Overview.bs

@@ -116,29 +116,43 @@ This specification does not mandate if and how scroll chaining or overscroll aff
 implemented. This specification only allows the content author to disable them if any are
 implemented.</em>
 
-<dfn>Scroll chaining</dfn> is when scrolling is propagated from one <a>scroll container</a> to an
-ancestor <a>scroll container</a> following the <a>scroll chain</a>. Typically scroll chaining is
-performed starting at the event target recursing up the <a>containing block chain</a>. When a
-<a>scroll container</a> in this chain receives a scroll event or gesture it may act on it and/or
-pass it up the chain. Chaining typically occurs when the <a>scrollport</a> has reached its boundary.
-
-A <dfn>scroll chain</dfn> is the order in which scrolling is propagated from one <a>scroll
-container</a> to another. The <a>viewport</a> participates in <a>scroll chaining</a> as the
-document's <a>scrollingElement</a>, both regarding placement in the scroll chain as well as adhering
-to the chaining rules applied to it.
-
-
-<dfn>Scroll boundary</dfn> refers to when the scroll position of a <a>scroll container</a> reaches
-the edge of the <a>scrollport</a>. If a [=scroll container=] has no potential to scroll, because it does
-not <a>overflow</a> in the direction of the scroll or the scroll does not happen in one of its [=scrollable axises=], the element is always considered to be at the
-scroll boundary.
-
-<dfn>Boundary default action</dfn> refers to the user-agent-defined <a>default action</a> performed
-when scrolling against the edge of the <a>scrollport</a>. A <dfn>local boundary default action</dfn>
-is a <a>boundary default action</a> which is performed on the <a>scroll container</a> without
-interacting with the page, for example displaying a overscroll UI affordance. Conversely, a
-<dfn>non-local boundary default action</dfn> interacts with the page, for example scroll chaining or
-a navigation action.
+<dfn>Scroll chaining</dfn> is when scrolling is propagated from one <a>scroll container</a>
+to an ancestor <a>scroll container</a>
+following the <a>scroll chain</a>.
+Typically scroll chaining is performed starting at the event target
+recursing up the <a>containing block chain</a>.
+When a <a>scroll container</a> in this chain receives a scroll event or gesture
+it may act on it and/or pass it up the chain.
+Chaining typically occurs when the <a>scrollport</a> has reached its boundary.
+
+A <dfn>scroll chain</dfn> is the order in which scrolling is propagated
+from one <a>scroll container</a> to another.
+For a given [=scroll container=] and scroll,
+the next link in its [=scroll chain=]
+is the nearest ancestor [=scroll container=]
+in the [=containing block chain=]
+that is scrollable in the scroll's axis.
+The <a>viewport</a> participates in <a>scroll chaining</a>
+as the document's <a>scrollingElement</a>,
+both regarding placement in the scroll chain
+as well as adhering to the chaining rules applied to it.
+
+<dfn>Scroll boundary</dfn> refers to when the scroll position of a <a>scroll container</a>
+reaches the edge of the <a>scrollport</a>.
+If a [=scroll container=] has no potential to scroll,
+because it does not <a>overflow</a> in the direction of the scroll,
+the element is always considered to be at the scroll boundary.
+If a [=scroll container=] is not scrollable in the given axis,
+it doesn't have a [=scroll boundary=] at all in that axis
+(and won't be part of this scroll's [=scroll chain=].)
+
+<dfn>Boundary default action</dfn> refers to the user-agent-defined <a>default action</a>
+performed when scrolling against the edge of the <a>scrollport</a>.
+A <dfn>local boundary default action</dfn> is a <a>boundary default action</a>
+which is performed on the <a>scroll container</a> without interacting with the page,
+for example displaying a overscroll UI affordance.
+Conversely, a <dfn>non-local boundary default action</dfn> interacts with the page,
+for example scroll chaining or a navigation action.
 
 
 
@@ -160,6 +174,10 @@ Note: This property should provide guarantees that are, at least, as strong as <
 for preventing both scroll chaining and overscroll. Doing otherwise would cause content authors to
 use <a>preventDefault</a> instead.
 
+
+The 'overscroll-behavior' Shorthand {#overscroll-shorthand}
+-----------------------------------
+
 <pre class=propdef>
 Name: overscroll-behavior
 Value: [ contain | none | auto | chain ]{1,2}