[xml] . vs self::node()

[Joachim Zobel <jz-2006 heute-morgen de>]

Hi.

I am using Libxml (2.6.32.dfsg-5 from debian) from the perl module. If I
am running a find in the context of a previously matched node

self::node()[ table:formula]//text:p

is accepted, while 

 [ table:formula]//text:p

gives me an "Invalid expression". Is this a bug or am I missing
something? 

Sincerewly,
Joachim