static parseTickTime_(rateInfo, text) {
    // 50t or 50.5t
    const results = shaka.text.TtmlTextParser.timeTickFormat_.exec(text);
    const ticks = Number(results[1]);

    return ticks / rateInfo.tickRate;
  }
Parses a TTML time in tick format.

@param {!shaka.text.TtmlTextParser.RateInfo_} rateInfo
@param {string} text
@return {?number}
@private