FloatingActionButtonのアニメーションを作っているMotionSpecって何？

<?xml version="1.0" encoding="utf-8"?>
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    Copyright 2017 The Android Open Source Project

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

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<set xmlns:android="http://schemas.android.com/apk/res/android">
  <objectAnimator
      android:propertyName="opacity"
      android:startOffset="0"
      android:duration="200"
      android:interpolator="@interpolator/mtrl_linear_out_slow_in"/>
  <objectAnimator
      android:propertyName="scale"
      android:startOffset="0"
      android:duration="200"
      android:interpolator="@interpolator/mtrl_linear_out_slow_in"/>
  <objectAnimator
      android:propertyName="iconScale"
      android:startOffset="0"
      android:duration="0"
      android:interpolator="@interpolator/mtrl_fast_out_slow_in"/>
</set>

import android.view.animation.Interpolator
import kotlin.math.sin

class CustomInterpolator : Interpolator {
    override fun getInterpolation(v: Float): Float {
        return sin(4 * v)
    }
}

val motionSpec = MotionSpec.createFromResource(this, R.animator.show)
motionSpec?.setTiming("scale", MotionTiming(0, 1000, CustomInterpolator()))
fab.showMotionSpec = motionSpec