Defined to 0 for compatibility with code written for older CMake versions that may have defined higher values.
Note
In CMake versions 2.8.2 through 2.8.12, this variable holds the fourth version number component of the CMAKE_VERSION variable.
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© 2000–2011 Insight Software Consortium
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.7/variable/CMAKE_TWEAK_VERSION.html