 all nodes in the DAG for that phase are evaluated.  For each root node that is true, the corresponding rules are injected.</p>
</dd>
</dl>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_expressions">Expressions</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Predicate expressions are trees.  The top of the tree, the "root", is usually associated with a rule: the rule will fire if and only if the associated root is true.  The leaves of the tree are usually literals.  The intermediate nodes repr