TSRef - TypoScript Reference
4.1.19. compatVersion
Syntax:
[compatVersion = x.y.z]
Comparison:
Require a minimum compatibility version. This version is not necessary equal with the TYPO3 version, it is a configurable value that can be changed in the Upgrade Wizard of the Install Tool.
"compatVersion" is especially useful if you want to provide new default settings but keep the backwards compatibility for old versions of TYPO3.