Upon creation, we check current OpenGL context abilities. Currently three support levels are possible: no support at all (old OpenGL), support through ARB extensions, or support built-in (newer OpenGL versions, >= 2.0).
All three cases are automatically handled inside, so usually you do not have to care about these details. Note that "none" support (on older OpenGL version with no appropriate ARB extensions) means that shaders are not really initialized at all.
Currently enabled GLSL program. Nil if fixed-function pipeline should be used. Setting this property encapsulates the OpenGL glUseProgram (or equivalent ARB extension), additionally preventing redundant glUseProgram calls.