code: private State checkh(State state) throws DatatypeException, IOException {
          if (state.context.length() == 0) {
              state = appendToContext(state);
          }
          state.current = state.reader.read();
          state = appendToContext(state);
          state = skipSpaces(state);
          boolean expectNumber = true;
  
          for (;;) {
              switch (state.current) {
                  default:
                      if (expectNumber)
                          reportNonNumber('h', state.current, state.context);
                      return state;
  
                  case '+':
                  case '-':
                  case '.':
                  case '0':
                  case '1':
                  case '2':
                  case '3':
                  case '4':
                  case '5':
                  case '6':
                  case '7':
                  case '8':
                  case '9':
                      break;
              }
              state = checkArg('h', "x coordinate", state);
  
              state = skipCommaSpaces2(state);
              expectNumber = state.skipped;
          }
      }
docs: Checks an 'h' command.