The [file] commands that talk to the OS (e.g. [file mtime]) start off being able to handle paths which enter and leave a VFS mount (e.g. but this capability seems to break once a relative path is used.

$ ./tclkit
% file mtime [file join [info nameofexecutable] ..]
1528994647
% file mtime .
1528994647
% file mtime [file join [info nameofexecutable] ..]
could not read not a directory