Mercurial has the ability to add new features through the use of extensions. Extensions may add new commands, add options to existing commands, change the default behavior of commands, or implement hooks. Extensions are not loaded by default for a variety of reasons: they can increase startup overhead; they may be meant for advanced usage only; they may provide potentially dangerous abilities (such as letting you destroy or modify history); they might not be ready for prime time; or they may alter some usual behaviors of stock Mercurial. It is thus up to the user to activate extensions as needed. To enable the "foo" extension, either shipped with Mercurial or in the Python search path, create an entry for it in your hgrc, like this:: [extensions] foo = You may also specify the full path to an extension:: [extensions] myfeature = ~/.hgext/myfeature.py To explicitly disable an extension enabled in an hgrc of broader scope, prepend its path with !:: [extensions] # disabling extension bar residing in /path/to/extension/bar.py bar = !/path/to/extension/bar.py # ditto, but no path was supplied for extension baz baz = !