getRegistered(type = false) {
    if (type) {
      return this.templateControlRegister[type] ?? undefined
    }
    return Object.keys(this.customRegister)
  }
Returns any custom fields that map to an existing type/subtype combination
@param  {string|false} type optional type of control we want to look up
subtypes of. If not specified will return all types
@return {Array|function} registered custom lookup keys