code: private State checkm(State state) throws DatatypeException, IOException {
          if (state.context.length() == 0) {
              state = appendToContext(state);
          }
          state.current = state.reader.read();
          state = appendToContext(state);
          state = skipSpaces(state);
  
          state = checkArg('m', "x coordinate", state);
          state = skipCommaSpaces(state);
          state = checkArg('m', "y coordinate", state);
  
          state = skipCommaSpaces2(state);
          boolean expectNumber = state.skipped;
          _checkl('m', expectNumber, state);
          return state;
      }
docs: Checks an 'm' command.