static getStyleAttributeFromRegion_(region, styles, attribute) {
    const TXml = shaka.util.TXml;
    const ttsNs = shaka.text.TtmlTextParser.styleNs_;

    if (!region) {
      return null;
    }

    const attr = TXml.getAttributeNSList(region, ttsNs, attribute);
    if (attr) {
      return attr;
    }

    return shaka.text.TtmlTextParser.getInheritedStyleAttribute_(
        region, styles, attribute);
  }
Finds a specified attribute on the element's associated region
and returns the value if the attribute was found.

@param {shaka.extern.xml.Node} region
@param {!Array<!shaka.extern.xml.Node>} styles
@param {string} attribute
@return {?string}
@private