code: Object getFunctionID(String key){
            Object id = m_functionID_customer.get(key);
            if (null == id) id = m_functionID.get(key);
            return id;
    }
docs: Obtain a function ID from a given function name
  @param key the function name in a java.lang.String format.
  @return a function ID, which may correspond to one of the FUNC_XXX values
  found in {@link org.apache.xpath.compiler.FunctionTable}, but may be a
  value installed by an external module.