The preset easing alias or a CSS <easing-function> string.
An options object affecting the output based on easingString.
If true, the returned easing function will be inverted.
An <easing-function> corresponding to the provided easingString.
"power1-in" or "bounce-out"), the returned <easing-function>
will be a custom <linear-easing-function> coming from a map of preset strings to linear easing functions.<easing-function> string (such as "ease-in" or "cubic-bezier(...)"), the string
itself will be returned with no modifications since it is obviously already a valid CSS easing function string.
Accepts either a preset easing alias (such as
"bounce-out") or a CSS<easing-function>string (such as"ease-in"or"cubic-bezier(...)") and returns an<easing-function>.