message: Add a meta scope to optional parameters
  It only applies to standard LaTeX commands.
  The scope is meta.parameter.optional.latex
diff: "name": "punctuation.definition.optional.arguments.begin.latex"
  },
  "2": {
  - "name": "variable.parameter.latex"
  + "name": "variable.parameter.function.latex"
  },
  "3": {
  "name": "punctuation.definition.optional.arguments.end.latex"
  }
  },
  - "match": "(\\[)([^\\[]*?)(\\])"
  + "match": "(\\[)([^\\[]*?)(\\])",
  + "name": "meta.parameter.optional.latex"
  }
  ]
  },
  