- patterns as arguments, which are matched against left-hand and
- right-hand, respectively, nodes of a relationship. Each of
- these can be used more than once, which means a unit name must
- match one of the given values.</para></listitem>
+ pattern as an argument, which will be matched against the
+ left-hand and the right-hand, respectively, nodes of a
+ relationship.</para>
+
+ <para>Each of these can be used more than once, in which case
+ the unit name must match one of the values. When tests for
+ both sides of the relation are present, a relation must pass
+ both tests to be shown. When patterns are also specified as
+ positional arguments, they must match at least one side of the
+ relation. In other words, patterns specified with those two
+ options will trim the list of edges matched by the positional
+ arguments, if any are given, and fully determine the list of
+ edges shown otherwise.</para></listitem>