https://android-dot-devsite-v2-prod.appspot.com/reference/androidx/constraintlayout/core/motion/utils/SplineSet.CustomSet
SplineSet.CustomSet | API reference | Android Developers
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https://developer.android.com/reference/androidx/constraintlayout/motion/utils/ViewTimeCycle.CustomSet?authuser=7
ViewTimeCycle.CustomSet | API reference | Android Developers
api referenceandroiddevelopers