Contains interfaces that extend Signature to provide
additional information about each possible join point signature.  This
additional information can be accessed by casting a Signature object
to the appropriate type, i.e.
  before(): call(* *(..)) {
      MethodSignature sig = (MethodSignature)thisJoinPoint.getSignature();
      ...
  }
This package also contains SourceLocation that provides
information about the location in source code that corresponds to a 
particular join point.