Add definition for composed live range

Author: dizhang168

dom.bs

@@ -22,6 +22,8 @@ urlPrefix: https://www.w3.org/TR/xml-names/#NT-
   text: QName; url: QName
 url: https://w3c.github.io/DOM-Parsing/#dom-range-createcontextualfragment
  type: method; text: createContextualFragment(); for: Range
+url: https://w3c.github.io/selection-api/#dom-selection-getrangeat
+ type: method; text: getRangeAt(); for: Range
 type: interface
  url: https://w3c.github.io/touch-events/#idl-def-touchevent
   text: TouchEvent
@@ -3027,6 +3029,14 @@ optional <i>suppress observers flag</i>, run these steps:
  <li><p>For each <a>live range</a> whose <a for=range>end node</a> is an <a>inclusive descendant</a>
  of <var>node</var>, set its <a for=range>end</a> to (<var>parent</var>, <var>index</var>).
 
+ <li><p>For each <a>composed live range</a> whose <a for=range>start node</a> is a
+ <a>shadow-including inclusive descendant</a> of <var>node</var>, set its <a for=range>start</a> to
+ (<var>parent</var>, <var>index</var>).
+
+ <li><p>For each <a>composed live range</a> whose <a for=range>end node</a> is an
+ <a>shadow-including inclusive descendant</a> of <var>node</var>, set its <a for=range>end</a> to
+ (<var>parent</var>, <var>index</var>).
+
  <li><p>For each <a>live range</a> whose <a for=range>start node</a> is <var>parent</var> and
  <a for=range>start offset</a> is greater than <var>index</var>, decrease its
  <a for=range>start offset</a> by 1.
@@ -5743,7 +5753,8 @@ are:
 <hr>
 
 <p>The <dfn method for=Document><code>createRange()</code></dfn> method steps are to return a new
-<a>live range</a> with (<a>this</a>, 0) as its <a for=range>start</a> an <a for=range>end</a>.
+{{Range}} <a>live range</a> with (<a>this</a>, 0) as its <a for=range>start</a> and <a
+for=range>end</a>.
 
 <p class=note>The {{Range/Range()}} constructor can be used instead.
 
@@ -7878,11 +7889,11 @@ range.setEnd(secondText, 4)
 <a>node tree</a> above cannot be represented by a <a>range</a>. <a>Ranges</a> are only useful for
 <a for=/>nodes</a>.
 
-<p>{{Range}} objects, unlike {{StaticRange}} objects, are affected by mutations to the
-<a>node tree</a>. Therefore they are also known as <a>live ranges</a>. Such mutations will not
-invalidate them and will try to ensure that it still represents the same piece of content.
-Necessarily, a <a>live range</a> might itself be modified as part of the mutation to the
-<a>node tree</a> when, e.g., part of the content it represents is mutated.
+<p>{{Range}} objects, unlike {{StaticRange}} objects, are affected by mutations to the <a>node
+tree</a>. Therefore they are <a>live ranges</a>. Such mutations will not invalidate them and will
+try to ensure that it still represents the same piece of content. Necessarily, a <a>live range</a>
+might itself be modified as part of the mutation to the <a>node tree</a> when, e.g., part of the
+content it represents is mutated.
 
 <p class=note>See the <a for=/>insert</a> and <a for=/>remove</a> algorithms, the
 {{Node/normalize()}} method, and the <a>replace data</a> and <a lt="split a Text node">split</a>
@@ -8109,12 +8120,22 @@ interface Range : AbstractRange {
 };
 </pre>
 
-<p>Objects implementing the {{Range}} interface are known as
-<dfn export id=concept-live-range>live ranges</dfn>.
+<p>A <dfn export id=concept-live-range>live range</dfn> is a <a>range</a> that is affected by
+mutations to the <a>node tree</a>.</p>
+
+<p>Objects implementing the {{Range}} interface are <a>live ranges</a>.
 
 <p class=note>Algorithms that modify a <a>tree</a> (in particular the <a for=/>insert</a>,
 <a for=/>remove</a>, <a>replace data</a>, and <a lt="split a Text node">split</a> algorithms) modify
-<a>live ranges</a> associated with that <a>tree</a>.
+<a>live ranges</a> associated with that <a>tree</a>.</p>
+
+<p>A <dfn export id=concept-composed-live-range>composed live range</dfn> is a <a>live range</a>
+that has one associated {{Range}} object - <dfn export
+id=concept-composed-live-range-cached-live-range for="composed live range">cached live
+range</dfn>.</p>
+
+<p class=note>The <a>cached live range</a> is used to maintain backward compatibility with the
+{{getRangeAt}} API.</p>
 
 <p>The <dfn export id=concept-range-root for="live range">root</dfn> of a <a>live range</a> is the
 <a for=tree>root</a> of its <a for=range>start node</a>.
@@ -8184,7 +8205,7 @@ but not its <a for=range>end node</a>, or vice versa.
 
 <dl class=domintro>
  <dt><code><var>range</var> = new <a constructor>Range()</a></code>
- <dd>Returns a new <a>live range</a>.
+ <dd>Returns a new {{Range}} <a>live range</a>.
 </dl>
 
 <p>The <dfn constructor for=Range lt="Range()"><code>new Range()</code></dfn> constructor steps are
@@ -8249,6 +8270,10 @@ steps:
 
      <li>Set <var>range</var>'s
      <a for=range>start</a> to <var>bp</var>.
+
+     <li>If <var>range</var> is the associated <a>cached live range</a> of a <a>composed live
+     range</a> <var>composed live range</var>, set <var>composed live range</var>’s <a
+     for="range">start</a> to <var>bp</var>.
     </ol>
    <dt>If these steps were invoked as "set the end"
    <dd>
@@ -8264,6 +8289,10 @@ steps:
 
      <li>Set <var>range</var>'s
      <a for=range>end</a> to <var>bp</var>.
+
+     <li>If <var>range</var> is the associated <a>cached live range</a> of a <a>composed live range</a>
+     <var>composed live range</var>, set <var>composed live range</var>’s <a for="range">end</a> to
+     <var>bp</var>.
     </ol>
   </dl>
 </ol>
@@ -8544,8 +8573,8 @@ method steps are:
  (<var>new node</var>, <var>new offset</var>).
 </ol>
 
-<p>To <dfn export id=concept-range-extract for="live range">extract</dfn> a <a>live range</a>
-<var>range</var>, run these steps:
+<p>To <dfn export id=concept-range-extract for="live range">extract</dfn> a {{Range}} <a>live
+range</a> <var>range</var>, run these steps:
 
 <ol>
  <li><p>Let <var>fragment</var> be a new {{DocumentFragment}} <a for=/>node</a> whose
@@ -8721,7 +8750,7 @@ method steps are:
    <li><a>Append</a> <var>clone</var>
    to <var>fragment</var>.
 
-   <li>Let <var>subrange</var> be a new <a>live range</a>
+   <li>Let <var>subrange</var> be a new {{Range}} <a>live range</a>
    whose <a for=range>start</a> is
    (<var>original start node</var>, <var>original start offset</var>) and
    whose <a for=range>end</a> is
@@ -8775,7 +8804,7 @@ method steps are:
    <li><a>Append</a> <var>clone</var>
    to <var>fragment</var>.
 
-   <li>Let <var>subrange</var> be a new <a>live range</a>
+   <li>Let <var>subrange</var> be a new {{Range}} <a>live range</a>
    whose <a for=range>start</a> is
    (<var>last partially contained child</var>, 0) and whose
    <a for=range>end</a> is
@@ -8800,7 +8829,7 @@ result of <a for="live range">extracting</a> <a>this</a>.
 
 <p>To
 <dfn export id=concept-range-clone for="live range" lt="clone the contents|cloning the contents">clone the contents</dfn>
-of a <a>live range</a> <var>range</var>, run these steps:
+of a {{Range}} <a>live range</a> <var>range</var>, run these steps:
 
 <ol>
  <li><p>Let <var>fragment</var> be a new {{DocumentFragment}} <a for=/>node</a> whose
@@ -8928,7 +8957,7 @@ of a <a>live range</a> <var>range</var>, run these steps:
    <li><a>Append</a> <var>clone</var>
    to <var>fragment</var>.
 
-   <li>Let <var>subrange</var> be a new <a>live range</a>
+   <li>Let <var>subrange</var> be a new {{Range}} <a>live range</a>
    whose <a for=range>start</a> is
    (<var>original start node</var>, <var>original start offset</var>) and
    whose <a for=range>end</a> is
@@ -8986,7 +9015,7 @@ of a <a>live range</a> <var>range</var>, run these steps:
    <li><a>Append</a> <var>clone</var>
    to <var>fragment</var>.
 
-   <li>Let <var>subrange</var> be a new <a>live range</a>
+   <li>Let <var>subrange</var> be a new {{Range}} <a>live range</a>
    whose <a for=range>start</a> is
    (<var>last partially contained child</var>, 0) and whose
    <a for=range>end</a> is
@@ -9006,7 +9035,7 @@ of a <a>live range</a> <var>range</var>, run these steps:
 result of <a for="live range">cloning the contents</a> of <a>this</a>.
 
 <p>To <dfn export id=concept-range-insert for="live range">insert</dfn> a <a for=/>node</a>
-<var>node</var> into a <a>live range</a> <var>range</var>, run these steps:
+<var>node</var> into a {{Range}} <a>live range</a> <var>range</var>, run these steps:
 
 <ol>
  <li>If <var>range</var>'s <a for=range>start node</a> is a {{ProcessingInstruction}} or {{Comment}}
@@ -9156,7 +9185,8 @@ check first thing, which matches everyone but Firefox.
 </ol>
 
 <p>The <dfn method for=Range><code>cloneRange()</code></dfn> method steps are to return a new
-<a>live range</a> with the same <a for=range>start</a> and <a for=range>end</a> as <a>this</a>.
+{{Range}} <a>live range</a> with the same <a for=range>start</a> and <a for=range>end</a> as
+<a>this</a>.
 
 <p>The <dfn method for=Range><code>detach()</code></dfn> method steps are to do nothing.
 <span class=note>Its functionality (disabling a {{Range}} object) was removed, but the method itself
@@ -10408,6 +10438,7 @@ David Håsäther,
 David Hyatt,
 Deepak Sherveghar,
 Dethe Elza,
+Di Zhang,
 Dimitri Glazkov,
 Domenic Denicola,
 Dominic Cooney,