Pre/Post behaviour
What a layer does before its first keyframe and after its last: hold still, repeat, bounce, or vanish.
Every layer's keyframes only cover a range of frames. Pre/Post behaviour decides what that layer does outside that range: before its first keyframe, and after its last one. Pre and Post are set independently, so a layer can hold before it starts and loop once it is done.
The four modes
| Mode | Before the first key | After the last key |
|---|---|---|
| Hold | Freezes on the first key's value | Freezes on the last key's value |
| Loop | Shows the tail of the cycle, as if it had already been repeating | Jumps back to the first key and repeats the same span, over and over |
| Ping Pong | Bounces back and forth across the range, as if it were already mid-bounce | Runs forward to the last key, reverses to the first, and keeps bouncing |
| None | The layer is not drawn at all | The layer is not drawn at all |
Hold is the default for both sides, precisely because None makes the layer vanish: a fresh layer should stay visible until you decide otherwise.
What None actually does
None does not mean "hold nothing" the way it might on a dropdown of blend modes. It means the layer is skipped entirely outside its key range: no fill, no stroke, nothing composited, as if the layer were hidden. This is the one mode that can make a layer disappear from the canvas without touching its Visible toggle.
Anything that reads this layer's pose for its own purposes, a bone chain bound to it, a mask, a cell lookup, still resolves it to the nearest boundary frame internally, even while it is invisible. That keeps the rest of a rig stable the moment the layer reappears, instead of snapping from a stale pose.
What the cycle repeats
Loop and Ping Pong repeat the span between a layer's very first keyframe and its very last, across every channel the layer owns: transform, vertices, style, bone keys, everything. If that span collapses to one frame or less, the mode simply holds on that frame instead of cycling.
Setting it
Right-click a layer row and open the Pre-Behaviour or Post-Behaviour submenu; each lists the four modes with a check mark on the active one. Small icons for both sit permanently in the Timeline's left gutter and past the last frame of every row, so you can see a layer's behaviour without opening the menu.
Showing the gutter
The Show Pre & Post Behaviors item in the View menu is off by default, so the gutter starts collapsed and the width goes to the rows instead. Turn it on when you need the icons; turn it back off if you never rely on anything but Hold.