With Tcl, it's always been possible to do that; Tcl is not Python or whatever.This sort of backwards compatibility exists with/is a feature of Tcl.Extensions built against 8.5 should be able to be loaded into 8.6 without problem.Certainly worth trying, imo.
Stu

    On Friday, September 20, 2024 at 09:29:54 a.m. EDT, Stuart Henderson <stu@spacehopper.org> wrote:  
 
 On 2024/09/20 12:43, Stuart Cassoff wrote:
> Private files aren't meant to be installed. They're in the 8.5 package mostly for historical
> reasons or older ports.
> Instead of using MODULES you could try setting BUILD_DEPENDS for 8.5 and WANTLIB and
> RUN_DEPENDS for 8.6.
> Something like that, maybe other vars as well.

That (building against private headers for an old Tk version which isn't
the version running the extension) seems like a worse idea than building
against current version private headers (whether they come from a :patch
target or from the package).