</context>
</xmlcode> runs ConTeXt on the fly. See also http://live.contextgarden.net/ for an online ConTeXt.
If you add <tt>source="yes"</tt> to the <context> tag, you have the source and the result displayed. Example:
<xmlcode><context source="yes">
\setupcolors [state=start]
\framed [background=color,
backgroundcolor=green,
offset=1cm ]{hello world!}
</context>
</xmlcode>