both
An option that displays the animation’s initial frame or final frame when playback occurs outside of the normal duration.
Declaration
static let both: AnimationFillModeDiscussion
For example, if you extend a hand-waving animation’s duration by one second in both directions by setting trimStart to -1.0, and trimEnd to duration + 1.0, a fillMode of both determines that the hand holds its initial appearance for one second before continuing to wave. Then, the animation freezes on its final hand-waving frame for one second before disappearing.