BBCode as plugin - how to protect from nested?

[matkus]

Hello.
I'm working on my first product for vB. It is custom BBCode, quite complicated to do, so I can't do it using simply "custom BBCodes" in ACP.
My BBCode works quite good already, but i have one problem.
I need to protect script from parsing nested BBCodes.
For example, if user will write [mybbcode][mybbcode]SOMETHING[/mybbcode][/mybbcode] it should not be parsed twice. The best would be, if only most nested code will be parsed, but if only most external one will be, it's OK for me too. Rest should be deleted or left as is, with BBCode not parsed.