Apart from hooks used during request processing, there are also hooks used for server configuration. Usually, each configuration hook is associated with a sole hook function and a specific configuration directive. Each such directive can be inserted into an Apache configuration file. Every time Apache parses the file and encounters the directive, the corresponding hook function is called.
The original set of Apache configuration directives can be easily extended. If we need to make our module configurable, we simply have to insert the extra directives (and the corresponding hook functions) into a special table. This table can be found among the module's administrative data structures.
There are also configuration hooks that are not related to any configuration directive. They are not limited to have only one associated hook function, either. These include a hook executed just before parsing the configuration file, and a hook executed once the parsing is finished. Intuitively, the former can be used to create data structures modified in the other configuration hooks, while the latter allows to initialize the data structures according to the current configuration.