There are lots of content that are deployed already. Changing the way the subtitle is displayed can break deployed content.

The below is an example that such change was implemented and later had to be reverted because it breaks deployed content

https://bugs.chromium.org/p/chromium/issues/detail?id=633690

CL to webvtt renderering engine should only change the display if there is a problem.

Therefore, I suggest, the following edits to the specification.

1. in session  7.2.10, under clause "If cue’s WebVTT cue snap-to-lines flag is false", step 2 should be removed. (this is not implemented)

2. specify that "lineAlign", "positionAlign" should be ignored. (then issue 633690 can be closed)

related discussion is also in https://bugs.chromium.org/p/chromium/issues/detail?id=314037#c11