def register():
    """Plugin registration."""
    if not plim:
        logger.warning('`slim` failed to load dependency `plim`. '
                       '`slim` plugin not loaded.')
        return
    if not mako:
        logger.warning('`slim` failed to load dependency `mako`. '
                       '`slim` plugin not loaded.')
        return
    if not bs:
        logger.warning('`slim` failed to load dependency `BeautifulSoup4`. '
                       '`slim` plugin not loaded.')
        return
    if not minify:
        logger.warning('`slim` failed to load dependency `htmlmin`. '
                       '`slim` plugin not loaded.')
        return

    signals.get_writer.connect(get_writer)