function readClosingTagName(source){
  let text = ""; //temporary data
  while(source.canRead()){
    let ch = source.readCh();
    // if (ch === null || ch === undefined) break;
    // source.updateBuffer();

    if (ch === ">") return text.trimEnd();
    else text += ch;
  }
  throw new Error(`Unexpected end of source. Reading '${substr}'`);
}
Read closing tag name
@param {Source} source
@returns tag name