code: public Method resolveFunction(String prefix, String localName)
      {
          if (_functions != null)
          {
              Function f = (Function) _functions.get(prefix + ":" + localName);
              return f.getMethod();
          }
          
          return null;
      }
docs: /*
  (non-Javadoc)
  
  @see javax.el.FunctionMapper#resolveFunction(java.lang.String, java.lang.String)