tango -D2 regex

[seany]

I dont find any info on backtrack on tango-D2 regex.

For example, I want to match things like
barFOObar

or

bazFOObaz

so I would use, in PCRE, ^(\w*)FOO($1)$, with $1 meaning the word 
(given by \w*  that was matced in the first subpattern (\w*)

How to do the samein Tango for D2 (or even phobos for D2)?