a list representing a regular
expression where the following reserved symbols are interpreted as
follows:
<a name="id3"></a></p>
<table class="tight"><tbody><tr>
<td valign="baseline" colspan="1" align="left">
</td><td valign="baseline" colspan="1" align="center"> <code>=</code> </td><td valign="baseline" colspan="1" align="left"> </td><td valign="baseline" colspan="1" align="left"> matches one occurrence in a 
<a href="ref-glossary.html#gl:space-instance">space-instance</a> path </td></tr>
<tr>
<td valign=