Note: Icap was removed from PHP. Neither this module, nor those versions of icap library are supported any longer. If you want to use calendar capabilities in PHP, use mcal instead.
The icap library has to be installed, which is not longer supported and available.
To get these functions to work, you have to compile PHP with --with-icap.
This extension has no configuration directives defined in php.ini.
This extension has no resource types defined.
This extension has no constants defined.