Feature request: output XML fragments #32

I have XML where the contents of some XML elements is HTML. I would like to collect the HTML literally as string. Since formatting XML is not trivial, I want to use XMLM output to stringify signals until I encounter an unmatched El_end. It is easy enough to pass the signals from the input to an output which writes to a buffer.

The issues is that the output writer doesn't accept fragments. It requires a Dtd and in case elements are followed by data I also need to output some outer element, which I do not want in the output and I have to strip later. All doable, but IMHO this is a reasonably frequent use case.

I think it would make sense to add an optional argument ~fragment to make_output or to allow fragments (that is no Dtd and elements followed by data) in case ~decl:false is passed to make_output, which (I think) indicates that one wants to have a fragment as result, so it would make sense to support fragments on input as well then.