Actions And Properties

Action shape

id, name, timing, properties, and targets are all required. The two that are easy to assume optional are not:

[REJECTED] An action with no timing, including a Set action that has nothing to time. Fragment: timelines.0.actions.0.timing: Required. Send timing: {duration: 0} on a Set.

[REJECTED] An action with no name. Fragment: timelines.0.actions.0.name: Required.

By contrast, trigger config.control is optional on a single-group interaction — config: {} is accepted and stored as-is, with nothing stamped. But omitting it is not the same as sending play: the runtime treats a missing control as restart. Send control: 'play' when you mean play. It becomes mandatory once the interaction has two or more action groups.

Tween type (tt)

Omit tt and the runtime treats it as To (0). presetId is optional — omit it on a new action; the host does not require one.

From (1) and FromTo (2) apply their starting values as soon as the timeline is built (GSAP immediate-render). That is the default, not a guarantee. The element then sits at the from-state until the trigger plays, so a From fade of opacity 0% → 100% looks missing on the canvas and on the published page until click, hover, or load. If the element should be visible at rest and animate on trigger, author a To (tt: 0 or omit).

The exception: buildTimeline scans each timeline in order and records every action’s properties per target, including a To. When a later From or FromTo touches a property an earlier action already recorded on the same target, that later action is built with immediateRender: false so it cannot overwrite the earlier action’s starting value while the paused timeline is built. In that case the element keeps its current state until playback, and the initial hidden state you expected at build time does not appear.

So a From is only reliably at its start value at rest when no earlier action in the same timeline targets the same property on the same target.

Choosing between From and FromTo for a reveal

Three rules in this pack point different ways on this, so state it once:

• A reveal — element hidden at rest, animating to whatever its stylesheet says — is a From (tt: 1) carrying only a from value: opacity: ['0%'] or ['0%', null]. GSAP animates from that value to the element’s live value, so there is no to to supply.
• Adding a to value to a From is a [PANEL-TRAP], not an error. It stores, and the panel’s To editor is disabled, so the user can neither see nor clear it. See panel-traps.md.
• Use FromTo (tt: 2) when you genuinely want both endpoints pinned, and the end state is not the element’s resting style — a hover that lifts to -8px and returns, for instance.

So “use tt: 1 for a reveal” and “use tt: 2 whenever the animation needs a start value” are both right, and neither means “send [from, to] on a From”.

The runtime reads only the slot your tt names

buildTweensForAction makes one GSAP call per tween type and hands it only the matching half of the config:

A [from, to] pair on a To is therefore built and then half discarded. GSAP animates from the element’s live computed value to to, not from the value you authored: scale: [0.55, 1.15] with tt: 0 on an unscaled element animates 1 → 1.15, and opacity: ['20%', '100%'] on an element that is already opaque animates nothing at all. The write succeeds, get_interaction echoes both values back, and no error is raised.

The Designer panel does mark it, though. Verified in the Interactions panel on an interaction stored with tt omitted and a [from, to] pair: the unused from field renders greyed out. So this is invisible to the API and to a read, but a human looking at the panel can see the discarded slot. If a user reports an animation that “does nothing”, pointing them at a greyed field is faster than re-reading the payload.

This is the most common reason a scroll-scrub payload looks inert: both endpoints are authored, one is used, and the visible delta is whatever sits between the element’s current state and the to value. Author tt: 2 whenever the animation needs a start value. Reserve tt: 0 for “from wherever it is now”.

The mirror case is dropped rather than half-applied. A To carrying only a from value (y: [40, null]) leaves config.to empty, and the action is skipped outright: if (tweenType === 0 && !hasToProps) continue.

The panel disables the editor for the unused slot, so the user cannot clear a stored value there either — see panel-traps.md.

A later From/FromTo does not park the element at its from-state

When two actions in the same interaction touch the same property on the same target — the usual hover in / hover out pair — only the first records a rest state. The second does not apply its from-value on load.

Verified on a published page with a two-trigger hover split: the leave action was tt: 2 with y: ['-8px', '0px'], and at rest the element measured translateY(0), not -8px. It moved 0 → -8 on enter and -8 → 0 on leave.

So authoring the out-direction as a FromTo mirror of the in-direction is safe inside one interaction, and does not leave the element visibly displaced before the user interacts. Two separate interactions have no such ordering relationship — there, prefer a To for the out-direction.

A from-state that collapses the element can make it unclickable

When the trigger element and the action target are the same element, the from-state is what the user has to interact with. A start value of scaleX: 0 or width: 0 leaves no box to hit, so a click or hover trigger on that element never fires; opacity: '0%' keeps the hit area but gives the user nothing to aim at. Both save cleanly and animate correctly once triggered — they just cannot be triggered.

Put the trigger on a parent that keeps its box and animate the child.

Non-animatable properties are only valid inside a Set action. The Designer always emits tt: 3 for them.

[REJECTED] A non-animatable property on a non-Set action. Guard: validateActionPropertyShape · fragment: is non-animatable and must only be used in a Set action

[LEGACY-OK-ON-UPDATE] Exactly two pairs are grandfathered on the update path: wf:class.class and wf:transform.display. Before Set actions shipped these could sit on a tt: 0 action mixed with animatable properties. An unchanged stored value passes through; a new or altered one is refused. The eligibility list is owned by the schema, so a caller flag cannot widen it to zIndex or anything else. Guard: isLegacyNonAnimatableGrandfatherEligible / shouldAllowLegacyNonAnimatableOnUpdate

Property namespaces

[REJECTED] A property name that is not on the allowlist for its extension key. Guard: validateActionPropertyShape · fragment: is not a supported

The message suggests the right namespace when you put a transform property under wf:style. The most common instance: opacity belongs under wf:transform, never wf:style.

Note rotation, not rotate.

wf:lottie, wf:spline, and wf:mouse-follow now carry their own property allowlists and are checked like any other key. They are in the generated table with their supported properties; do not assume a plugin namespace skips validation.

Every action key the API can author now has an entry, so in practice nothing skips the property-name check today. The fallback still exists for a key added to the registry before its allowlist, and the namespace gate handles unknown extension keys either way.

wf:class — the Class operation

The only wf:class property is class, and it is non-animatable, so it lives in a Set action (tt: 3). The value is null (unset / reset — the runtime treats it as a no-op) or an object carrying both keys:

operation is addClass / removeClass / toggleClass. selectors is an array of non-empty style-block id strings.

selectors is not combo-expanded. Unlike a wf:class target value, where the host walks the chain and adds the combo’s parents for you, a selectors entry applies exactly the one class it names. Verified on a published page: passing the combo leaf id for is-featured turned class="pg-card" into class="pg-card is-featured" — the leaf and nothing else. So name the class you want applied, and if the visual result depends on a parent already being present, make sure the element carries it.

Every rejection below comes from validateWfClassPropertyValue, except the last.

[REJECTED] A property name other than class under wf:class. Guard: validateActionPropertyShape · fragment: is not a supported

[REJECTED] A bare array or string value. Fragment: value must be null or an object {operation, selectors}

[REJECTED] An extra key alongside operation / selectors. Fragment: does not support property

[REJECTED] Only one of the two keys. Fragment: must include both "operation" and "selectors"

[REJECTED] An operation outside the three. Fragment: operation must be one of addClass, removeClass, toggleClass

[REJECTED] selectors not an array, or containing an empty string. Fragments: selectors must be an array of style-block id strings and must be an array of non-empty style-block id strings

[REJECTED] The whole property on an animated tween. Because class is non-animatable it is Set-only. Guard: validateActionPropertyShape · fragment: non-animatable and must only be used in a Set action (tt: 3)

Guessing this shape from the tool schema costs four round trips — each message is precise, but they only arrive one at a time.

timing.autoReverse is not authorable

Covered in envelope-and-targets.md alongside the other fields the Designer never writes. Short version: [REJECTED] on both action.timing.autoReverse and timeline.settings.autoReverse, with an unchanged stored value allowed through on update.

Value shapes

Accepted: a bare scalar, [from], [from, to], [from, null], [null, to], or a random/additive wrapper.

[REJECTED] A plain {from, to} object. The Designer never stores one. Guard: validateActionPropertyShape · fragment: must not be a plain {from, to} object

That rule is namespace-scoped, not global. It holds for wf:transform, wf:style, and wf:class. It is inverted for two plugin namespaces: wf:lottie.lottie and every wf:spline channel require a {from?, to?} object and refuse an array. Read as an absolute, this rule makes both namespaces unauthorable. See the plugin value shapes below.

wf:style value shapes

Seven properties, in two groups. The three colours animate; the other four do not and are Set-only (tt: 3).

Note the asymmetry worth remembering: display is non-animatable but lives under wf:transform, while these four are non-animatable and live under wf:style. Non-animatable is a property fact, not a namespace fact.

Colour and rotation value formats

Colours are hex strings. The three wf:style colour properties (backgroundColor, borderColor, color) take '#rrggbb'. Verified accepted as a bare scalar ('#1a1a2e') and as a [from, to] pair; the pair is what interpolates, and ['#ffffff', '#f2eee6'] was measured animating a published body to rgb(242, 238, 230). A bare scalar on a To reads the to slot and tweens from the element’s live colour.

Rotation is in degrees, as a bare number. rotation: [0, 8] is eight degrees, not radians and not a 'deg' string. Verified by measurement: the published element reported matrix(0.990268, 0.139173, …), which is cos 8° / sin 8°.

On a Set action, a bare scalar is enough

A Set (tt: 3) reads only the to slot, and a bare scalar occupies it. Both of these are accepted and applied at runtime — verified on a published page, where .pg-card went from display: block to display: none:

Prefer the bare scalar on a Set: there is no from-state to express, so a pair invites the reader to think the first value does something. display takes a CSS display keyword as a string; 'none' and 'block' are both confirmed.

wf:lottie value shapes

Two properties. Both are validated; neither takes the tuple form used everywhere else.

Every rejection comes from validateLottieNested.

[REJECTED] An array, or any non-object. Fragment: value must be an object with from/to

[REJECTED] Only one of the two. Fragment: must include both "from" and "to"

[REJECTED] A key other than from / to / manualDuration. Fragment: supported keys: from, to, manualDuration

[REJECTED] A non-numeric from / to. Fragment: from/to must be numbers or variable references

[REJECTED] A non-boolean manualDuration, at either level. Fragment: must be a boolean

wf:spline value shapes

Three properties.

The fourteen channels: positionX positionY positionZ rotationX rotationY rotationZ scaleX scaleY scaleZ intensity opacity zoom color stateName.

Note the asymmetry with wf:lottie: a spline channel takes {from?, to?} with both optional, while lottie requires both. Every rejection comes from validateSplineNested.

[REJECTED] An array, or any non-object, for spline. Fragment: value must be an object of animatable channels

[REJECTED] A channel name outside the fourteen. Fragment: does not support channel — the message then lists all fourteen, which is the only place that list appears at runtime.

[REJECTED] A channel given a tuple or scalar instead of an object. Fragment: must be a {from?, to?} object

[REJECTED] A field other than from / to inside a channel. Fragment: only supports from/to fields

Random and additive

The Designer stores Random and Relative wrappers as the to leaf of a [from, to] tuple, so capability checks run per authored leaf rather than only on a top-level wrapper.

Wrapper shapes

Three wrappers. The unit is always its own field — never baked into the value. That is the one that costs attempts: {type: 'ix3-additive', value: '40px'} is refused, because value is numeric and px belongs in unit.

ix3-additive composes: {type: 'ix3-additive', value: {type: 'ix3-random', min: 0, max: 10}} emits +=random(0, 10).

[REJECTED] A wrapper missing a required field. Fragments: malformed ix3-random, malformed ix3-additive, malformed ix3-random-array. These name the wrapper but not the missing field, so check the table above rather than guessing variants.

[REJECTED] ix3-random-array on a property that does not support random values. Fragment: does not support random values

[REJECTED] ix3-random min/max on a property that supports only value sets. Colors are value-set only. Fragment: does not support random min/max range values

[REJECTED] ix3-additive on a property that does not support it. Colors do not. Fragment: does not support additive values

[REJECTED] A random-array outside the size bounds (see the generated file). Fragment: random-array must have between

[REJECTED] A wrapper carrying a known type discriminator that fails its structural guard. Fragment: has a malformed

timing.duration — seconds, not milliseconds

secondsOrMsSchema stores a consistent number of seconds. Two input forms:

• A number is already seconds. 0.4 is four hundred milliseconds. 400 is four hundred seconds.
• A "Nms" string is converted: "400ms" becomes 0.4.

The built-in presets use 0.3. The panel’s unit toggle writes either a number of seconds or an "Nms" string; it never writes a millisecond number. The write succeeds either way — nothing will tell you that duration: 400 is six minutes forty seconds.

[REJECTED] at schema: '1.5s', a bare '400', or any other string form. Fragment: Milliseconds must be in format "123ms" or "123.45ms"

A third input form exists and is easy to miss: secondsOrMsSchema also accepts null, and transforms it to 0.25. That is not the same as omitting the field, which leaves it unset and lets the runtime default apply. Do not send null expecting “no duration”.

timing.delay on an action is accepted and then ignored

timingConfigSchema declares delay: z.number() but ends with .merge(playbackSettingsSchema), whose delay is the seconds-or-ms union, and a Zod merge overrides the earlier key. So "400ms" is accepted on delay and normalizes to 0.4. Read the merge before trusting a field’s declared type on this schema.

But the value does nothing on an action. buildTweensForAction builds its GSAP tween vars from position, duration, stagger, repeat, and repeatDelay. It never reads action.timing.delay. The write succeeds, get_interaction echoes the value back, and the animation is unaffected. Nothing reports it.

Delay is real in the two other places it appears:

To stagger actions inside a timeline, use timing.position, not timing.delay.

On a percent canvas the same field is authored as a percent — see timelines-and-groups.md.

timing.position — the Start field

The panel treats position as an absolute start time. It writes either a number of seconds or an "Nms" string, depending on the unit toggle, and Reset clears it. There is no operator UI.

Two layers refuse different things here, and they return different errors.

Schema first. timelinePositionSchema accepts a number, an "Nms" string, a GSAP alignment operator (<, >), a relative operator (+=0.5), or an alignment with offset (<+=1.5). Anything else fails before a guard runs.

[REJECTED] at schema: '1.5s', a bare '500', or any other string form. Fragment: Absolute position must be a number or milliseconds string

Then the guard. The operator forms the schema allows are the ones the panel cannot author or display: getTimelineEditorInputValue returns null for them, so the Start field renders empty and the next edit silently overwrites the operator with an absolute time.

[REJECTED] at the guard: <, >, +=0.5, <+=1, and the other operator forms. Guard: findActionTimingPositionError · fragment: is not a start time the Designer can author

These two split across the layers as well, despite both being non-finite:

[REJECTED] at schema: NaN. Zod’s z.number() refuses it during parsing, so it never reaches the guard. Fragment: Invalid input

[REJECTED] at the guard: Infinity and -Infinity. Zod accepts both as numbers because the position schema does not apply .finite(), so the guard is what stops them. The Start field only writes finite seconds. Guard: findActionTimingPositionError

The guard tests !Number.isFinite, which covers NaN too, but that branch is unreachable through a normal parse and is defensive only.

If you are matching an error, check which layer produced it. A schema failure names the expected format; the guard names the Designer.

On a percent canvas the same field is authored as a percent — see timelines-and-groups.md.

timing.ease — the Ease field

ease is a number, not a string. easeConfigSchema is z.union([z.number().int().nonnegative(), advancedEaseSchema]).

This one is worth reading carefully, because the rejection teaches you nothing. It is a Zod union failure, so the message is a bare Invalid input at timing.ease with no branch detail and no enum — the only non-enumerating validation message on this surface. A dogfood run spent seven attempts on it (four string forms, a bezier array, two object shapes) and never landed it.

[REJECTED] Any string: 'power1.out', 'power2.out', 'ease-out', 'linear'. Layer: Zod (easeConfigSchema) · fragment: Invalid input

[REJECTED] A 4-number bezier array such as [0.25, 0.1, 0.25, 1]. customBezierSchema exists but is deprecated and is not part of easeConfigSchema. Use {type: 'customEase', bezierCurve}.

[SILENTLY-DROPPED] easing in place of ease. timingConfigSchema is a non-strict object, so the misspelling is stripped and the animation ships with default easing. Nothing reports it. Same failure mode as the trigger config strip in envelope-and-targets.md.

Built-in easing index

The integer indexes EASING_NAMES in packages/systems/ix3/runtime/src/utils.ts. The panel’s “Linear” is 0; its “Power 1 out” is 2.

Advanced eases

Objects discriminated on type, each .strict(). Authorable — just write one. A {type: 'back', curve: 'out', power: 1.7} ease was accepted and stored on a live site, and no guard rejects an advanced ease at the write boundary.

No write-boundary guard rejects an advanced ease. Nothing to check before writing one.

curve is in / out / inOut. taper is none / in / out / both. wiggleType is easeOut / easeInOut / anticipate / uniform / random. templateCurve is a "family.direction" string; the rough set covers every family, the expoScale set omits back / bounce / circ / elastic.

timing.stagger.ease takes the identical union.

[PANEL-TRAP] timing.ease on a Set action. The Ease row is not rendered for Set, so a stored value is invisible and uneditable.

timing.stagger — the Stagger block

staggerConfigSchema is an object. A bare number is rejected.

[REJECTED] A bare number for stagger. Layer: Zod · fragment: Expected object, received number

[REJECTED] grid: 'none'. The panel’s Grid “None” is the absent / null state, not a string. Layer: Zod · fragment: Invalid input

[REJECTED] stagger.ease as a string, per the ease rules above.

[PANEL-TRAP] stagger on a Set action — the repeat / yoyo / stagger / splitText block is gated behind a non-Set tween type.

splitText

splitText is an action-level field, a sibling of timing, properties, and targets — not timing.splitText. Getting that wrong is a [SILENTLY-DROPPED], not a rejection: timingConfigSchema is non-strict, so a misplaced splitText is stripped and the text ships unsplit with no error.

Where the panel-trap table lists “timing.repeat / yoyo / stagger / splitText on a Set action”, the first three are timing keys and the fourth is not; they share a trap, not a parent.

The target needs text, not a particular element type

The constraint is that copy exists inside the target — in the element itself or a descendant. It is not that the target be a Heading, Paragraph, or Text. Verified on a published page: a Block whose text is a child String node (.pg-card containing “Card one”) produced two gsap_split_word spans, while a Paragraph in the same run produced twenty.

What does fail is a target with no text anywhere inside it. That saves, reads back intact, and animates nothing — no error, because nothing structural is wrong with the payload.

The Mask dropdown offers “None” plus the option matching the split type, and choosing None omits mask rather than storing a value. So the only object forms the panel writes are {type} or {type, mask} with the two equal.

Two layers again.

[REJECTED] at schema: mask: 'none', or any value outside the mask enum. splitTextMaskSchema is z.enum(['chars', 'words', 'lines']).optional(), so 'none' never reaches the guard. Choosing None in the panel omits mask rather than storing a value, which is why there is no 'none' member. Omit the key instead.

[REJECTED] at the guard: an otherwise valid mask that differs from type. Guard: findActionSplitTextError · fragment: must match

[REJECTED] The legacy string form (splitText: 'chars') on create. The panel reads it for migration but no longer writes it. Guard: findActionSplitTextError

[LEGACY-OK-ON-UPDATE] A stored string survives an update when the same action id echoes the same value. Two extra conditions apply: a duplicated action id is refused outright, so one stored string cannot authorize a second row claiming the same id, and changing the value re-enters the reject.

Pass a stored string through untouched. Author the object form for anything new.

SplitText needs a target that contains text, whether directly or in a descendant. The runtime hands the resolved element to GSAP SplitText, which walks child elements, so a Div wrapping a Paragraph that reads “Hello” is a valid target and still yields character targets. You do not need to add a text element, or retarget to the inner one, just to make splitting work.

What does split nothing is a target with no text anywhere inside it. An empty Div or Block saves cleanly and then animates nothing. Creating a Block and trying to set_text onto it is the wrong fix; point the action at something that already holds copy. The write path does not check element type.

Panel traps

These are accepted by the write path and invisible in the panel afterwards.

[PANEL-TRAP] timing.duration on a Set action. The panel disables the Duration input for Set, but no guard rejects a stored non-zero duration.

[PANEL-TRAP] timing.ease on a Set action. The Ease row is not rendered for Set.

[PANEL-TRAP] timing.repeat, timing.yoyo, timing.stagger, or splitText on a Set action. The whole block is gated behind a non-Set tween type in the panel.

[PANEL-TRAP] A from slot value on a To tween, or a to slot value on a From tween. The corresponding editor is disabled, so the user cannot clear what you stored. validateActionPropertyShape checks leaf shapes, not slot-versus-tween consistency.