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