GLSL Compatibility

The GLSL shading language varies across versions of OpenGL.

WebGL 1.0, admits the OpenGL ES Shading Language, Version 1.00, and WebGL 2.0 admits the OpenGL ES Shading Language, Version 3.00.

I think that many authors will want their pxl programs to be portability to the web, so ensuring that we only allow the GLSL subset that WebGL 1.0 accepts may be desirable. Or, perhaps allow authors to opt-into whatever the system version of GLSL is.