Added in version 3.14.
Tells what mode the current running script is in. Could be one of several values:
PROJECTRunning in project mode (processing a CMakeLists.txt file).
SCRIPTRunning in -P script mode.
FIND_PACKAGERunning in --find-package mode.
CTESTRunning in CTest script mode.
CPACKRunning in CPack.
The CMAKE_SCRIPT_MODE_FILE variable.