The <defs> section permits pseudoelements to be defined. The pseudoelement facility allows an element with name x and attribute/value pair a=b to be considered as if it were an element y. The <defs> section may contain any number of <pseudoelement> definitions. The syntax of a <pseudoelement> definition is:
<pseudoelement name="y">Pseudoelements are very useful in defining rendering rules for the <content-view> and <tree-view> sections.
<element name="x"/>
<attr-value name="a" value="b"/>
</pseudoelement>