_getSharedOptions(start, mode) {
    const firstOpts = this.resolveDataElementOptions(start, mode);
    const previouslySharedOptions = this._sharedOptions;
    const sharedOptions = this.getSharedOptions(firstOpts);
    const includeOptions = this.includeOptions(mode, sharedOptions) || (sharedOptions !== previouslySharedOptions);
    this.updateSharedOptions(sharedOptions, mode, firstOpts);
    return {sharedOptions, includeOptions};
  }
@todo v4, rename to getSharedOptions and remove excess functions