Define overflow clip

issue#351

index.bs

@@ -60,6 +60,8 @@ urlPrefix: https://drafts.csswg.org/cssom-view-1/
  url: #pinch-zoom; type:dfn; text: pinch zoom
 urlPrefix: https://drafts.csswg.org/css2/visuren.html
  url: #viewport; type:dfn; text: viewport
+urlPrefix: https://drafts.csswg.org/css-overflow-3/
+ url: #overflow-properties; type:dfn; text: overflow properties
 </pre>
 
 <pre class="link-defaults">
@@ -305,6 +307,8 @@ or else the <a>top-level browsing context</a>'s {{document}} node
 (referred to as the <dfn for="IntersectionObserver">implicit root</dfn>) if
 the {{IntersectionObserver/root}} attribute is <code>null</code>.
 
+An {{Element}} is defined as having an <dfn for="IntersectionObserver">overflow clip</dfn> if its computed style has <a>overflow properties</a> that cause its content to be clipped to the element's padding edge.
+
 The <dfn for=IntersectionObserver>root intersection rectangle</dfn>
 for an {{IntersectionObserver}}
 is the rectangle we'll use to check against the targets.
@@ -316,7 +320,7 @@ is the rectangle we'll use to check against the targets.
  <dt>If the <a>intersection root</a> is a {{document}},
  <dd>it's the size of the {{document}}'s <a>viewport</a> (note that this processing step can only be reached if the {{document}} is <a>fully active</a>).
 
- <dt>Otherwise, if the <a>intersection root</a> has an overflow clip,
+ <dt>Otherwise, if the <a>intersection root</a> has an <a>overflow clip</a>,
  <dd>it's the element's <a>content area</a>.
 
  <dt>Otherwise,
@@ -592,7 +596,7 @@ run these steps:
  of the {{document}}, and update |container| to be
  the <a>browsing context container</a> of |container|.
  2. Map |intersectionRect| to the coordinate space of |container|.
- 3. If |container| has overflow clipping or a css <a>clip-path</a> property,
+ 3. If |container| has an <a>overflow clip</a> or a css <a>clip-path</a> property,
  update |intersectionRect| by applying |container|'s clip.
  4. If |container| is the root element of a <a>browsing context</a>,
  update |container| to be the <a>browsing context</a>'s {{document}};