https://www.khronos.org/registry/webgl/extensions/WEBGL_draw_instanced_base_vertex_base_instance/ and https://www.khronos.org/registry/webgl/extensions/WEBGL_multi_draw_instanced_base_vertex_base_instance/ are draft WebGL extensions offering the BaseVertex / BaseInstance functionality commonly supported by lower-level graphics APIs, including OpenGL.
These extensions are well supported in ANGLE, supported in Chromium behind a flag, and need to be similarly exposed in WebKit's WebGL implementation behind a flag in order to demonstrate to the WebGL working group that they're supportable in multiple browser implementations.
Committed 251862@main (ad4e2e1bb0cb): <https://commits.webkit.org/251862@main>
Reviewed commits have been landed. Closing PR #1767 and removing active labels.