Apply the function to the list of nodes passed as arguments and return the result as type T.
Throws IllegalArgumentException if the function cannot be applied to the nodes passed as argument
or the number of arguments is not correct.
context - the context of the execution. Same as using the
NodeSelector '.' as parameter.
A string describing the signature of this node function, e.g. "fn:content(uris : Nodes) : Nodes". The
syntax for representing the signature can be chosen by the implementer. This method is for informational