self::para selects the context node if it is a para element, and otherwise selects nothing
<?xgrep-match [xgrep-test1.xml]--------------------------------?>
<para name="para1" type="zzz">
    something
	<div><para name="para1b"/></div>
  </para>
<?xgrep-match [xgrep-test1.xml]--------------------------------?>
<para name="para2" type="warning"/>
<?xgrep-match [xgrep-test1.xml]--------------------------------?>
<para name="lastPara" type="warning"/>