bp_core_get_illegal_names( array|string $value = '', array|string $oldvalue = '' )

function bp_core_get_illegal_names( $value = '', $oldvalue = '' ) {

	// Make sure $value is array.
	if ( empty( $value ) ) {
		$db_illegal_names = array();
	}

	if ( is_array( $value ) ) {
		$db_illegal_names = $value;
	} elseif ( is_string( $value ) ) {
		$db_illegal_names = explode( ' ', $value );
	}

	// Add the core components' slugs to the banned list even if their components aren't active.
	$bp_component_slugs = array(
		'groups',
		'members',
		'forums',
		'blogs',
		'activity',
		'profile',
		'friends',
		'search',
		'settings',
		'notifications',
		'register',
		'activate'
	);

	// Core constants.
	$slug_constants = array(
		'BP_GROUPS_SLUG',
		'BP_MEMBERS_SLUG',
		'BP_FORUMS_SLUG',
		'BP_BLOGS_SLUG',
		'BP_ACTIVITY_SLUG',
		'BP_XPROFILE_SLUG',
		'BP_FRIENDS_SLUG',
		'BP_SEARCH_SLUG',
		'BP_SETTINGS_SLUG',
		'BP_NOTIFICATIONS_SLUG',
		'BP_REGISTER_SLUG',
		'BP_ACTIVATION_SLUG',
	);
	foreach( $slug_constants as $constant ) {
		if ( defined( $constant ) ) {
			$bp_component_slugs[] = constant( $constant );
		}
	}

	/**
	 * Filters the array of default illegal usernames.
	 *
	 * @since BuddyPress 1.2.2
	 *
	 * @param array $value Merged and unique array of illegal usernames.
	 */
	$filtered_illegal_names = apply_filters( 'bp_core_illegal_usernames', array_merge( array( 'www', 'web', 'root', 'admin', 'main', 'invite', 'administrator' ), $bp_component_slugs ) );

	/**
	 * Filters the list of illegal usernames from WordPress.
	 *
	 * @since BuddyPress 3.0
	 *
	 * @param array Array of illegal usernames.
	 */
	$wp_filtered_illegal_names = apply_filters( 'illegal_user_logins', array() );

	// First merge BuddyPress illegal names.
	$bp_merged_names           = array_merge( (array) $filtered_illegal_names, (array) $db_illegal_names );

	// Then merge WordPress and BuddyPress illegal names.
	$merged_names              = array_merge( (array) $wp_filtered_illegal_names, (array) $bp_merged_names );

	// Remove duplicates.
	$illegal_names             = array_unique( (array) $merged_names );

	/**
	 * Filters the array of default illegal names.
	 *
	 * @since BuddyPress 1.2.5
	 *
	 * @param array $value Merged and unique array of illegal names.
	 */
	return apply_filters( 'bp_core_illegal_names', $illegal_names );
}