With the following example, the output xml writer fails to properly 
transform & to the html entity & in some urls; \hyphenatedurl works 
fine.

The generated xhtml and html files have this problem as well as more 
issues with the transformation, including what appears to be mistaken 
transformation of < and > to html entities and unbalanced <link> tags.

When a URL without & is used, the problems do not appear.

I used the default export-example.css file, and I assume that the lack 
of interaction in the result reflects the lack of coding for links in 
that file.

This was tested with the 2014-08-27 standalone.

    \setupbackend[export=xmltest.xml,xhtml=xmltest.xhtml,css=export-example.css]
    \setupinteraction[state=start]
    \useURL[avecAmpersand]
    [http://www.mail-archive.com/search?l=ntg-context@ntg.nl&q=Epub]
       [][klik hier]
    \starttext
    \startsubject[title=Fails in xml]
    \startparagraph
       \tex{from}: \from[avecAmpersand]
    \stopparagraph
    \startparagraph
       \tex{goto&[url]}: \goto{klik
    hier}[url(http://www.mail-archive.com/search?l=ntg-context@ntg.nl&q=Epub)]
    \stopparagraph
    \stopsubject
    \startsubject[title=Okay in xml]
    \startparagraph
       \tex{url}: \url[avecAmpersand]
    \stopparagraph
    \startparagraph
       \tex{hyphenatedurl}:
    \hyphenatedurl{http://www.mail-archive.com/search?l=ntg-context@ntg.nl&q=Epub}
    \stopparagraph
    \stopsubject
    \stoptext

-- 
Rik Kabel