gl.h constants definitions

This probably sounds pretty stupid but,are the constants defined in gl.h (like say GL_TEXTURE_2D) common(i.e. do they have the same value) among different implementations of opengl?They should or else apps compiled with one implementation might not work with the other but I haven’t seen anything about them in the specs(not that I have looked much).
Also do they remain constant when new versions of opengl come out.

The value of the constants are the same on all implementtions, and they keep their value over new versions of OpenGL.

most of the consants are values to the GLenum data type.