[cssom-view] Define 'beginning of the document' for navigating to #top. https://www.w3.org/Bugs/Public/show_bug.cgi?id=15588

Author: Simon Pieters

cssom-view/Overview.html

@@ -125,7 +125,9 @@ <h2 class="no-num no-toc" id="toc">Table of Contents</h2>
    <li><a href="#css-pixels"><span class="secno">3.1 </span>CSS pixels</a></ol></li>
  <li><a href="#common-infrastructure"><span class="secno">4 </span>Common Infrastructure</a>
   <ol class="toc">
-   <li><a href="#scrolling"><span class="secno">4.1 </span>Scrolling</a></ol></li>
+   <li><a href="#scrolling"><span class="secno">4.1 </span>Scrolling</a>
+    <ol class="toc">
+     <li><a href="#common-scroll-positions"><span class="secno">4.1.1 </span>Common Scroll Positions</a></ol></ol></li>
  <li><a href="#extensions-to-the-window-interface"><span class="secno">5 </span>Extensions to the <code title="">Window</code> Interface</a>
   <ol class="toc">
    <li><a href="#the-mediaquerylist-interface"><span class="secno">5.1 </span>The <code title="">MediaQueryList</code> Interface</a></li>
@@ -261,8 +263,8 @@ <h2 id="terminology"><span class="secno">3 </span>Terminology</h2>
  <dd><p>Righward and upward.
 </dl>
 
-<p>The term <dfn id="scrolling-area">scrolling area</dfn> refers to a box of an element that has the following edges, depending on the element's scrolling box's <a href="#overflow-directions">overflow
-directions</a>.
+<p>The term <dfn id="scrolling-area">scrolling area</dfn> refers to a box of a <a href="#viewport">viewport</a> or an element that has the following edges, depending on the
+<a href="#viewport">viewport</a>'s or element's scrolling box's <a href="#overflow-directions">overflow directions</a>.
 
 <dl class="switch">
  <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and downward
@@ -384,6 +386,28 @@ <h3 id="scrolling"><span class="secno">4.1 </span>Scrolling</h3>
 <p>When a user agent is to perform an <dfn id="concept-instant-scroll" title="concept-instant-scroll">instant scroll</dfn> of a scrolling box <var title="">box</var> to
 <var title="">position</var>, it must update the scroll position of <var title="">box</var> to <var title="">position</var>.
 
+<h4 id="common-scroll-positions"><span class="secno">4.1.1 </span>Common Scroll Positions</h4>
+
+<p>The <dfn id="beginning-of-the-document">beginning of the document</dfn> is the scroll position the <a href="#viewport">viewport</a> would have by aligning the <a href="#scrolling-area">scrolling area</a> in the
+<a href="#viewport">viewport</a> as follows, depending on the <a href="#viewport">viewport</a>'s <a href="#overflow-directions">overflow directions</a>:
+
+<dl class="switch">
+ <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and downward
+ <dd><p>Align the top edge of the <a href="#scrolling-area">scrolling area</a> with the top of the <a href="#viewport">viewport</a>. Align the left edge of the <a href="#scrolling-area">scrolling area</a>
+ with the left of the <a href="#viewport">viewport</a>.
+ <dt>If the <a href="#overflow-directions">overflow directions</a> are leftward and downward
+ <dd><p>Align the top edge of the <a href="#scrolling-area">scrolling area</a> with the top of the <a href="#viewport">viewport</a>. Align the right edge of the <a href="#scrolling-area">scrolling area</a>
+ with the right of the <a href="#viewport">viewport</a>.
+ <dt>If the <a href="#overflow-directions">overflow directions</a> are leftward and upward
+ <dd><p>Align the bottom edge of the <a href="#scrolling-area">scrolling area</a> with the bottom of the <a href="#viewport">viewport</a>. Align the right edge of the <a href="#scrolling-area">scrolling
+ area</a> with the right of the <a href="#viewport">viewport</a>.
+ <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and upward
+ <dd><p>Align the bottom edge of the <a href="#scrolling-area">scrolling area</a> with the bottom of the <a href="#viewport">viewport</a>. Align the left edge of the <a href="#scrolling-area">scrolling
+ area</a> with the left of the <a href="#viewport">viewport</a>.
+</dl>
+
+<p class="note">The <a href="#beginning-of-the-document">beginning of the document</a> concept is used when navigating to the <code title="">#top</code> fragment identifier, as defined in HTML.
+<a href="#refsHTML">[HTML]</a>
 
 <h2 id="extensions-to-the-window-interface"><span class="secno">5 </span>Extensions to the <code title="">Window</code> Interface</h2>
 

cssom-view/Overview.src.html

@@ -231,8 +231,8 @@ <h2>Terminology</h2>
  <dd><p>Righward and upward.
 </dl>
 
-<p>The term <dfn>scrolling area</dfn> refers to a box of an element that has the following edges, depending on the element's scrolling box's <span>overflow
-directions</span>.
+<p>The term <dfn>scrolling area</dfn> refers to a box of a <span>viewport</span> or an element that has the following edges, depending on the
+<span>viewport</span>'s or element's scrolling box's <span>overflow directions</span>.
 
 <dl class=switch>
  <dt>If the <span>overflow directions</span> are rightward and downward
@@ -354,6 +354,28 @@ <h3>Scrolling</h3>
 <p>When a user agent is to perform an <dfn title=concept-instant-scroll>instant scroll</dfn> of a scrolling box <var title>box</var> to
 <var title>position</var>, it must update the scroll position of <var title>box</var> to <var title>position</var>.
 
+<h4>Common Scroll Positions</h4>
+
+<p>The <dfn>beginning of the document</dfn> is the scroll position the <span>viewport</span> would have by aligning the <span>scrolling area</span> in the
+<span>viewport</span> as follows, depending on the <span>viewport</span>'s <span>overflow directions</span>:
+
+<dl class=switch>
+ <dt>If the <span>overflow directions</span> are rightward and downward
+ <dd><p>Align the top edge of the <span>scrolling area</span> with the top of the <span>viewport</span>. Align the left edge of the <span>scrolling area</span>
+ with the left of the <span>viewport</span>.
+ <dt>If the <span>overflow directions</span> are leftward and downward
+ <dd><p>Align the top edge of the <span>scrolling area</span> with the top of the <span>viewport</span>. Align the right edge of the <span>scrolling area</span>
+ with the right of the <span>viewport</span>.
+ <dt>If the <span>overflow directions</span> are leftward and upward
+ <dd><p>Align the bottom edge of the <span>scrolling area</span> with the bottom of the <span>viewport</span>. Align the right edge of the <span>scrolling
+ area</span> with the right of the <span>viewport</span>.
+ <dt>If the <span>overflow directions</span> are rightward and upward
+ <dd><p>Align the bottom edge of the <span>scrolling area</span> with the bottom of the <span>viewport</span>. Align the left edge of the <span>scrolling
+ area</span> with the left of the <span>viewport</span>.
+</dl>
+
+<p class=note>The <span>beginning of the document</span> concept is used when navigating to the <code title>#top</code> fragment identifier, as defined in HTML.
+<span data-anolis-ref>HTML</span>
 
 <h2>Extensions to the <code title>Window</code> Interface</h2>