setDxfGroup = (reader, line) => {
  // groups are numeric
    const code = parseInt(line)
    if (isNaN(code)) {
      emiterror(reader, 'Invalid group (int)')
      reader.group = null
    } else {
      reader.group = code
    }
  }
Parse the given line in the context of the given reader, and update the group
@param reader {DxfReader} - context DxfReader to use
@param line {String} - line to parse