The type of VTTRegion.lines is changed to unsigned long in https://github.com/w3c/webvtt/issues/414, and VTTRegion.lines no longer throws IndexSizeError when set negative value due to the change.
Pull request: https://github.com/WebKit/WebKit/pull/17585
Committed 267827@main (dc25ee48a22a): <https://commits.webkit.org/267827@main> Reviewed commits have been landed. Closing PR #17585 and removing active labels.
<rdar://problem/115215420>