def _key_split(matchobj):
    """Expands a {key a+b+c} syntax into <span class="key">a</span> + ...

    More explicitly, it takes a regex matching {key ctrl+alt+del} and returns:
    <span class="key">ctrl</span> + <span class="key">alt</span> +
    <span class="key">del</span>

    """
    keys = [k.strip() for k in matchobj.group(1).split('+')]
    return ' + '.join(['<span class="key">%s</span>' % key for key in keys])