[CMake] Simple example of IMPILICIT_DEPENDS?

[lists_ravi at lavabit.com]

Hello,
  Does anyone have a reasonably simple example of using add_custom_command
with IMPLICIT_DEPENDS that invokes the CXX scanner? The two examples I
found via Google do not lead themselves to easy simplification.
  My goal is to run a custom command that takes as arguments some
explicitly named .h and .cpp files; the custom command needs to be rerun
every time when one of the named files or any of their dependencies
change. It appears that IMPLICT_DEPENDS was created to solve exactly
this problem, but I haven't been able to make this work:
  http://www.cmake.org/pipermail/cmake/2009-November/033218.html

Are there any unit tests for CMake that test that IMPLICIT_DEPENDS works
correctly with the CXX scanner?

Regards,
Ravi