This rule allows the definition of custom rules using XPath expressions.
Issues are created depending on the return value of the XPath expression. If the XPath expression returns:
  -  a single or list of AST nodes, then a line issue with the given message is created for each node 
-  a boolean, then a file issue with the given message is created only if the boolean is true 
-  anything else, no issue is created 
Here is an example of an XPath expression to log an issue on each 'td' tag using the 'nowrap' deprecated attribute:
//td[@nowrap]