function scopeSugar(mode) {
  if (mode.scope && typeof mode.scope === "object" && mode.scope !== null) {
    mode.beginScope = mode.scope;
    delete mode.scope;
  }
}
this exists only to allow `scope: {}` to be used beside `match:`
Otherwise `beginScope` would necessary and that would look weird

  {
    match: [ /def/, /\w+/ ]
    scope: { 1: "keyword" , 2: "title" }
  }
@param {CompiledMode} mode