Reliably trapping end of paragraph / return to vertical mode

[Taylor, P]

William F Hammond wrote:

>
> Nonetheless, without full justification, my guess is that if
> one were writing software to format a suitable XML document
> type (which could be profiled LaTeX in the sense of my 2010
> TUG talk) to either regular LaTeX or plainTeX, one would not
> have great trouble knowing whether a new paragraph has been
> entered.

Agreed, and for large documents (books, etc), XML is my markup of 
choice.  But I am trying to write my floating figures code to 
accommodate raw TeX users, and one can never know quite how devious they 
will be, so I am trying to write defensively.  Would you not agree that 
this is a worthwhile aim ?

** Phil.