PRIVATE_HEADER
--------------

Specify private header files in a :prop_tgt:`FRAMEWORK` shared library target.

Shared library targets marked with the :prop_tgt:`FRAMEWORK` property generate
frameworks on macOS, iOS and normal shared libraries on other platforms.
This property may be set to a list of header files to be placed in the
PrivateHeaders directory inside the framework folder.  On non-Apple
platforms these headers may be installed using the ``PRIVATE_HEADER``
option to the ``install(TARGETS)`` command.
