<<a>> and [[a]] not supported.

[cmal]

<> and [[a]] not supported.

Is <<a>> org syntax? As for [[a]] if should be working but you do have to implement your own link parsing for anything other than raw paths/URIs. So if your link is [[file:/foo/bar]] you need to implement the parsing of that to an actual file.

[rasendubi]

Yes, it's org syntax. <> is a radio target and [[a]] is a radio link. These are currently not implemented indeed

Oh, I thought radio targets were a triplet of < > not a pair.

https://orgmode.org/manual/Radio-Targets.html

Huh, this is called a "dedicated link". I'd not ever heard of that.

https://orgmode.org/manual/Internal-Links.html