+
+typedef void ExtFunc();
+
+/** Indicates whether an extension is supported. */
+bool is_supported(const std::string &);
+
+/** Returns the OpenGL version number, as reported by the implementation. */
+const Version &get_gl_version();
+
+/** Indicates whether the OpenGL version is at least a.b. */
+bool is_version_at_least(unsigned a, unsigned b);
+
+/** Returns the address of an extension function. Only indended for internal
+use. */