Add validity criteria for StaticRange objects

dom.bs

@@ -7650,6 +7650,21 @@ constructor steps are:
  <var>init</var>["{{StaticRangeInit/endOffset}}"]).
 </ol>
 
+<p>A {{StaticRange}} is <dfn for=StaticRange export>valid</dfn> if all of the following are true:
+
+<ul>
+ <li><p>Its <a for=range>start</a> and <a for=range>end</a> are in the same <a>node tree</a>.
+
+ <li><p>Its <a for=range>start offset</a> is between 0 and its <a for=range>start node</a>'s
+ <a>length</a>, inclusive.
+
+ <li><p>Its <a for=range>end offset</a> is between 0 and its <a for=range>end node</a>'s
+ <a>length</a>, inclusive.
+
+ <li><p>Its <a for=range>start</a> is <a for="boundary point">before</a> or
+ <a for="boundary point">equal</a> to its <a for=range>end</a>.
+</ul>
+
 
 <h3 id=interface-range>Interface {{Range}}</h3>
 
@@ -10013,6 +10028,7 @@ Chris Paris,
 Chris Rebert,
 Cyrille Tuzi,
 Dan Burzo,
+Daniel Clark,
 Daniel Glazman,
 Darin Fisher,
 David Bruant,