chapter[title] selects the chapter children of the context node that have one or more title children
<?xgrep-match [xgrep-test1.xml]--------------------------------?>
<chapter>
	  <title name="t1">Title</title>
	  <title name="t2">Introduction</title>
	  <title name="t3"/>
	</chapter>
<?xgrep-match [xgrep-test1.xml]--------------------------------?>
<chapter>
	  <title/>
	</chapter>