[CMake] "Copy if Different" question

[Michael Jackson]

if I have the following code:

EXECUTE_PROCESS(COMMAND ${CMAKE_COMMAND}
   -E copy_if_different ${TEMP_CONFIG_FILE} ${HDF5_BINARY_DIR}/ 
H5pubconf.h)

How exactly is "Different" determined? By date modified, by content,  
by some sort of hash?
_________________________________________________________
Mike Jackson                  mike.jackson at bluequartz.net
BlueQuartz Software                    www.bluequartz.net
Principal Software Engineer                  Dayton, Ohio