pause() {
    if (!this.parent) {
      return false;
    }
    if (!this._activePrompt) {
      return false;
    }
    if (!this._midPrompt) {
      return false;
    }
    const val = this._lastDelimiter + this._activePrompt.rl.line;
    this._midPrompt = false;
    const rl = this._activePrompt.screen.rl;
    const screen = this._activePrompt.screen;
    rl.output.unmute();
    screen.clean();
    rl.output.write('');
    return val;
  }
Pauses active prompt, returning
the value of what had been typed so far.

@return {String} val
@api public