Should texSubImage2D's type match the texture's type if texture's format is unsized?

In WebGL1 / ES2, because it takes format/type to fully specify a texture's format, it is required texSubImage2D's format/type has to match the texture's format/type.

In WebGL2 / ES3, we don't have such constraints for sized textures, because the internalformat itself defines the texture's format, so as far as texSubImage2D's format/type and the texture's internalformat are compatible, the call is valid.

However, what about textures with unsized formats? Should we match the behavior with WebGL1, i.e., require both format/type to match?

Begin by comparing the WebGL1/ES2 and WebGL2/ES3 rules for texSubImage2D, focusing on unsized texture formats and format/type compatibility. The work is done when the expected behavior is decided and the relevant specification text or issue guidance clearly records that rule.

Written by the indexing model from the issue text.