> + * Plugins wishing to re-register themselves, e.g. with a different priority,
+ * should first unregister themselves using @c plugin_extension_unregister()
+ * and call @c plugin_extension_register() afterwards.
+ * 
+ * @param extension The @c PluginExtension structure instance provided by the
+ * plugin.
+ * @param ext_name Human-readable name of the extension that can appear in
+ * the user interface. The string should be reasonably unique so extensions can
+ * be distinguished from each other.
+ * @param priority The higher number, the earlier in the extension list the
+ * plugin is and the higher chance it becomes called when multiple extensions
+ * compete for the same feature.
+ * @param data User data passed to the functions from the @c PluginExtension
+ * struct.
+ * @warning Plugins are responsible for calling @c plugin_extension_unregister()
+ * when they no longer provide the extension.