Consider the following XML document:

<test><!-- a --><somenode><!-- b --></somenode><!-- c --></test>

and let libxml2 evaluate the XPath expression "//comment()" on it.
libxml2 returns node-set (a,c,b) instead of (a,b,c), that I would have
expected. To be exact, "(//comment())[2]" gives singleton (c) instead of
the expected (b).
W3C's XPath recommendation indeed states, that predicates are to
determine "the position of the node in the node-set ordered in document
order if the axis is a forward axis" [1], which should be the case here.

On Wed, 2006-10-18 at 17:26 -0400, Daniel Veillard wrote:
> There is a good workaround, call xmlXPathOrderDocElems() on your
> document before running XPath queries on it, that fixes it and will
> speed up some XPath operations a lot. 

Confirmed, that works for the time being.

Thanks!
Marius