code: public static boolean isValidFormat( String key ) {
          if (StringUtil.isBlank(key) || key.length() <= IDENTIFIER_START_INDEX) return false;
          return true;
      }
docs: Determine if the supplied string may be a valid identifier. This method returns 'false' only if the identifier is known to
  be invalid (e.g., it is not of the correct format). This method may return true even if the identifier itself does not
  reference an existing node.
  
  @param key
  @return true if the string is of the correct format for a node key, or false if it not the correct format