Previously classes like "underline" and "marked" had to
be the first class in a span in order for the span to be
interpreted as a "ul" or "mark" element. This commit allows
these special classes to be "stacked," e.g.
`[test]{.mark .underline}`; in addition, the special classes are no
longer required to come first in the list of classes.
See #8194 for context.
