Ensure that all WebGL specific behavioral changes are documented.

WebGL introduces behavioral changes to the underlying specifications (often in areas where undefined underlying behaviors exist).

Ensure that all such changes (new errors, semantic changes, etc.) are documented at least with a reference to the underlying specification sections and text exerpt as applicable, or failing to that, with a reasoning (in case of other incompatibilities like severe performance drawbacks, widespread driver errors or D3D compatibility issues).

The issue names no files, tests, or entry points. Start by inventorying WebGL-specific behavioral changes, then trace each change to the underlying specification sections and relevant text. Done means every change is documented with a specification reference and excerpt, or with reasoning for incompatibilities such as performance, driver, or D3D issues.

Written by the indexing model from the issue text.