VTTCue - Web APIs
vttcue.snaptolines returns true if the vttcue.line attribute is an integer number of lines or a percentage of the video size.
...this can be the string auto or a number whose interpretation depends on the value of vttcue.snaptolines.

Web Video Text Tracks Format (WebVTT) - Web APIs
region; attribute directionsetting vertical; attribute boolean snaptolines; attribute (double or autokeyword) line; attribute linealignsetting linealign; attribute (double or autokeyword) position; attribute positionalignsetting positionalign; attribute double size; attribute alignsetting align; attribute domstring text; documentfragment getcueashtml(); }; vtt region interface this is the second interface in webvtt api.