Timed Text is text with timecodes, most common as subtitles. Timed text files can be recognized by the extension XML. There are dozens of XML formats for subtitling. All of them quite similar, but in fact slightly different.
Often our clients don't even know which XML they require. We do. Recently a new standard for timed text has been released: EBU-TT. An initiative of the European Broadcasting Union (EBU).