+<li>MESA_EXTENSION_MAX_YEAR - The GL_EXTENSIONS string returned by Mesa is sorted
+by extension year.
+If this variable is set to year X, only extensions defined on or before year
+X will be reported.
+This is to work-around a bug in some games where the extension string is
+copied into a fixed-size buffer without truncating.
+If the extension string is too long, the buffer overrun can cause the game
+to crash.
+This is a work-around for that.
+<li>MESA_GL_VERSION_OVERRIDE - changes the value returned by
+glGetString(GL_VERSION) and possibly the GL API type.
+<ul>
+<li> The format should be MAJOR.MINOR[FC]
+<li> FC is an optional suffix that indicates a forward compatible context.
+This is only valid for versions >= 3.0.
+<li> GL versions < 3.0 are set to a compatibility (non-Core) profile
+<li> GL versions = 3.0, see below
+<li> GL versions > 3.0 are set to a Core profile
+<li> Examples: 2.1, 3.0, 3.0FC, 3.1, 3.1FC
+<ul>
+<li> 2.1 - select a compatibility (non-Core) profile with GL version 2.1
+<li> 3.0 - select a compatibility (non-Core) profile with GL version 3.0
+<li> 3.0FC - select a Core+Forward Compatible profile with GL version 3.0
+<li> 3.1 - select a Core profile with GL version 3.1
+<li> 3.1FC - select a Core+Forward Compatible profile with GL version 3.1
+</ul>
+<li> Mesa may not really implement all the features of the given version.
+(for developers only)
+</ul>
+<li>MESA_GLSL_VERSION_OVERRIDE - changes the value returned by
+glGetString(GL_SHADING_LANGUAGE_VERSION). Valid values are integers, such as
+"130". Mesa will not really implement all the features of the given language version
+if it's higher than what's normally reported. (for developers only)
+<li>MESA_GLSL - <a href="shading.html#envvars">shading language compiler options</a>