What TTML stores
TTML (Timed Text Markup Language) is the W3C's XML format for timed text. Each lyric line is a <p> with a begin and end time. For word-synced lyrics, every word sits inside the line as its own <span> with its own begin and end, so a player can light words up as they are sung.
Choose line timing for one paragraph per line, or word timing for a span on every word. Unlike plain LRC, each word carries a real end time.