This class is the abstract base class for all RichText function handlers. A function handler is responsible for a certain function such as ‘example’ or ‘query’. functions are used in internal RichText references such as ’[[example:Allocation 2]]’. ‘example’ is the function, ‘Allocation’ is the path and ‘2’ is the first argument. Arguments are optional. The function handler can turn such internal references into Strings or XMLElement trees. Therefor, each derived handler needs to implement a to_s, to_html and to_tagged method that takes two parameter. The first is the path, the second is the argument Array.