For plugin authors, an API is available for retrieving and manipulating roles and capabilities. A plugin can create a new capability called ‘do_foo’ and give that capability to the Adminstrator role with the following code.
$role = get_role('administrator');
$role->add_cap('do_foo');
To check if the currently logged in user has this capability, plugins can make use of the current_user_can() function.
if ( current_user_can('do_foo') ) ...
To check the capabilities for a certain user ID, instantiate a WP_User object.
$user_id = 1;
$user = new WP_User($user_id);
if ( $user->has_cap('do_foo') ) ...
If a brand new role is needed, one can be created using add_role() and add_cap().
$role = add_role('foo_doer', 'Foo Doer');
$role->add_cap('do_foo');
$role->add_cap('do_bar');
