New in version 3.18.
Read-only property indicating of whether an ALIAS target is globally visible.
The boolean value of this property is TRUE for aliases to IMPORTED targets created with the GLOBAL options to add_executable() or add_library(), FALSE otherwise. It is undefined for targets built within the project.
Note
Promoting an IMPORTED target from LOCAL to GLOBAL scope by changing the value or IMPORTED_GLOBAL target property do not change the scope of local aliases.
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https://cmake.org/cmake/help/v3.19/prop_tgt/ALIAS_GLOBAL.html