First selector: Clarified behavior

Fixes gh-894
Closes gh-895

Author: AurelioDeRosa

entries/first-selector.xml

@@ -5,7 +5,7 @@
   <signature>
     <added>1.0</added>
   </signature>
-  <desc>Selects the first matched element.</desc>
+  <desc>Selects the first matched DOM element.</desc>
   <longdesc>
     <p>The <code>:first</code> pseudo-class is equivalent to <code>:eq( 0 )</code>. It could also be written as <code>:lt( 1 )</code>. While this matches only a single element, <a href="/first-child-selector/">:first-child</a> can match more than one: One for each parent.</p>
   </longdesc>