Oracle 10g and regular expressions

i am trying to make an document in oracle 10g database and looking for regular expressions for syntax.
but i had a problem at collating elements the problem is i couldnt understand it in an article saying this

For example, to find the collating sequence 'ch', use the following regular expression:
[[.ch.]]
This expression matches the sequence 'ch' in the following string:
chabc
The expression does not match the following string:
cdefg
(from http://64.233.183.104/search?q=cache:OOkidAdtazYJ:www.stanford.edu/dept/itss/docs/oracle/10g/appdev.101/b10795/adfns_re.htm+nested+regular+expressions+in+oracle&hl=tr&gl=tr&ct=clnk&cd=3)
but i couldnt run this can anybody help me