[cmake-developers] why can target_include_directories() not be applied to custom targets?

[Drew Parsons]

Commit 510fdcb18801076e2041eaae2941375eecc93ec2 at
https://gitlab.kitware.com/cmake/cmake/commit/510fdcb18801076e2041eaae2941375eecc93ec2
prevents custom targets from using target_include_directories().

This makes no sense to me.  A custom target is still a target. It needs
to be compiled, it uses -I flags.

Can you explain the ban on applying target_include_directories() to
custom targets?

Drew