+<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|COMPAT]
+ <li>FC is an optional suffix that indicates a forward compatible
+ context. This is only valid for versions >= 3.0.
+ <li>COMPAT is an optional suffix that indicates a compatibility
+ context or GL_ARB_compatibility support. This is only valid for
+ versions >= 3.1.
+ <li>GL versions <= 3.0 are set to a compatibility (non-Core)
+ profile
+ <li>GL versions = 3.1, depending on the driver, it may or may not
+ have the ARB_compatibility extension enabled.
+ <li>GL versions >= 3.2 are set to a Core profile
+ <li>Examples: 2.1, 3.0, 3.0FC, 3.1, 3.1FC, 3.1COMPAT, X.Y, X.YFC,
+ X.YCOMPAT.
+ <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 GL version 3.1 with GL_ARB_compatibility enabled
+ per the driver default.
+ <li>3.1FC - select GL version 3.1 with forward compatibility and
+ GL_ARB_compatibility disabled.
+ <li>3.1COMPAT - select GL version 3.1 with GL_ARB_compatibility
+ enabled.
+ <li>X.Y - override GL version to X.Y without changing the profile.
+ <li>X.YFC - select a Core+Forward Compatible profile with GL
+ version X.Y.
+ <li>X.YCOMPAT - select a Compatibility profile with GL version
+ X.Y.
+ </ul>
+ <li>Mesa may not really implement all the features of the given
+ version. (for developers only)
+</ul>
+<li>MESA_GLES_VERSION_OVERRIDE - changes the value returned by
+glGetString(GL_VERSION) for OpenGL ES.
+<ul>
+<li> The format should be MAJOR.MINOR
+<li> Examples: 2.0, 3.0, 3.1
+<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_CACHE_DISABLE - if set to `true`, disables the GLSL shader cache
+<li>MESA_GLSL_CACHE_MAX_SIZE - if set, determines the maximum size of
+the on-disk cache of compiled GLSL programs. Should be set to a number
+optionally followed by 'K', 'M', or 'G' to specify a size in
+kilobytes, megabytes, or gigabytes. By default, gigabytes will be
+assumed. And if unset, a maximum size of 1GB will be used. Note: A separate
+cache might be created for each architecture that Mesa is installed for on
+your system. For example under the default settings you may end up with a 1GB
+cache for x86_64 and another 1GB cache for i386.
+<li>MESA_GLSL_CACHE_DIR - if set, determines the directory to be used
+for the on-disk cache of compiled GLSL programs. If this variable is
+not set, then the cache will be stored in $XDG_CACHE_HOME/mesa_shader_cache (if
+that variable is set), or else within .cache/mesa_shader_cache within the user's
+home directory.