How to extend packages

Hi, Ada-folks!

I'd like to extend the GNAT.Regpat a little bit, so that it contains
additional operations like Split (the same as in Perl or Ruby) or Join
(dito).

When speaking of "extending" I mean it in the sense of e.g. Java where
extending a class means that the child class contains all the public
or protected operations and attributes as the super class. Perhaps you
know now, what I want to achieve. I want to have an extended "child"
package of GNAT.Regpat. In the end it should have an own name like
e.g. "Mine.Regex" and contain all operation etc. of its "super"
package plus the operations I'll additionally implement.

I've been trying for hours now, so I'm passing this question to you.
How to extend package?

Thanks,
Matthias