Certain elements have default styles or behaviors that make certain combinations likely to lead to confusion. Where these have equivalent alternatives without this problem, the confusing combinations are disallowed.
div elements are rendered as block boxes, and span elements as inline boxes. Putting a block box in an inline box is unnecessarily confusing; since either nesting just div elements, or nesting just span elements, or nesting span elements inside div elements all serve the same purpose as nesting a div element in a span element, but only the latter involves a block box in an inline box, the latter combination is disallowed."> The current version builds fine for me.
> $ wget "http://home.ccil.org/~cowan/XML/tagsoup/tagsoup-1.2-src.zip"
> $ unzip tagsoup-1.2-src.zip
> $ cd tagsoup-1.2
> $ export CLASSPATH=~/.m2/repository/xalan/xalan/2.7.0/xalan-2.7.0.jar #
> Default Java on Snow Leopard isn't picking up a TransformerFactory
> $ ant
Good. The key is to always use ant.
> I'm not sufficiently familiar with HTML5 to say whether disallowed means
> silently dropped or an error happens.
Neither.  It means that HTML authors who intend to conform to HTML5
MUST NOT do something.  It does not necessarily mean that the behavior
of a HTML5-conforming browser is to report an error, or even that the
behavior is not defined by HTML5.