Oracle Regex Patterns

Question

I have 3 Regex patterns from oracle 10/11 that I need to port to oracle 9. However, I am getting different results when I try to do the matching. Is there a way to fix this ? Is it even possible to port these patterns and get the same results when matching ?

Here are the patterns:

'^[[:alnum:]\_]$' which I would think would map to '[A-Za-z0-9_]*$'

'^[[:alpha:]]$' which i would think would map to '^[A-Za-z]*$'

'^(\"|\'')' which I would think needs to map over into 2 patterns '^["]*$' or '^['']*$'

owa pattern docs

oracle 10g regex docs

EDIT: So my question was originally part of a lexor that was giving me trouble in a parser..it turns out my problem was related to a type (and not the regex) ..My regex patterns match close enough(and actually I changed the :alnum to use "\w" instead of the other pattern.)

There's one thing I still don't understand what does double enclosing brackets mean [[ with in the example regex ?