Delphi RTL, is it allowed in "pure-blood" Island?

Delphi SysUtils provides quite a few utility methods that ISLAND RTL currently does not.
For example, I didn’t find Delphi SysUtils.ExtractFileDir counterpart in Island RTL.

It is good that we have DelphiRTL to help convert legacy Delphi code - but my question is: for brand new Island application writing from scratch, in a situation like this, should I use DelphiRTL to mix with Island RTL for convenience, or should I write the pure-blood Island code meaning I may re-inventing wheels?

Sorry I guess this is not a technical questions, but a religious question. But I’d like to hear advice.

As for your example, try to use the the Path Class.
The Elements RTL aka RTL2 is a rich Cross Platform Library.
For new Code I would only use the RTL2.
Spend some Time with it, it’s worth to do so.
I think the DelphiRtl is nice to have for legacy code, but for new Code, don’t use it.