This rule allows to define some homemade Erlang rules with help of an XPath expression.
Violations are created depending on the return value of the XPath expression. If the XPath expression returns:
<li>a single or list of AST nodes, then a line violation with the given message is created for each node</li>
<li>a boolean, then a file violation with the given message is created only if the boolean is true</li>
<li>anything else, no violation is created</li>
Here is an example of an XPath expression to log a violation on each if expression : //ifExpression