fix(parsers): splitting a clip keeps keyframes the parser cannot read (#5044)

* fix(parsers): splitting a clip keeps keyframes the parser cannot read

* refactor(parsers): keyframed split branch in its own function

* fix(parsers): no writer rewrites keyframes it cannot read; a split reports an unknown start

* fix(parsers): recast property edits keep keyframes they cannot read

* fix(parsers): keyframe edits refuse unreadable object keyframes at the one locator

* style(parsers): shorten the unroll safety comment

* fix(parsers): a split never invents a start value from unreadable keyframes

* fix(parsers): object keyframe steps that are named, spread or number-keyed are unreadable

* fix(parsers): array steps, getters, stray channels and unresolved array values read as unreadable keyframes

packages/parsers/src/gsapParser.ts

@@ -22,6 +22,7 @@ import {
   safeJsKey as safeKey,
   resolveConversionProps,
   mergePercentageKeyframes,
+  authorsKeyframes,
 } from "./gsapSerialize";
 
 export type {
@@ -1551,7 +1552,7 @@ export function updateAnimationInScript(
     return script;
   }
   const target = parsed.located.find((l) => l.id === animationId);
-  if (!target) return script;
+  if (!target || (updates.properties && target.animation.hasUnresolvedKeyframes)) return script;
   applyUpdatesToCall(target.call, updates);
   return recast.print(parsed.ast).code;
 }
@@ -1943,14 +1944,14 @@ export function splitAnimationsInScript(
     const dur = anim.duration ?? 0;
     const animEnd = pos + dur;
 
-    if (anim.keyframes) {
+    if (authorsKeyframes(anim)) {
       if (pos >= opts.splitTime) {
         result = updateAnimationSelector(result, anim.id, newSelector);
       } else if (animEnd > opts.splitTime) {
         // Spanning keyframes can't be correctly split without renormalizing
         // percentages and durations — leave on original, warn the caller.
         skippedSelectors.push(`${originalSelector} (keyframes spanning split)`);
-        const kfs = anim.keyframes.keyframes;
+        const kfs = anim.keyframes?.keyframes ?? [];
         for (const kf of kfs) {
           const kfTime = pos + (kf.percentage / 100) * dur;
           if (kfTime <= opts.splitTime) {
@@ -1961,7 +1962,10 @@ export function splitAnimationsInScript(
         }
       } else {
         // Entirely before split — extract final keyframe properties
-        const kfs = anim.keyframes.keyframes;
+        if (anim.hasUnresolvedKeyframes) {
+          skippedSelectors.push(`${originalSelector} (unreadable keyframes before split)`);
+        }
+        const kfs = anim.keyframes?.keyframes ?? [];
         if (kfs.length > 0) {
           for (const [k, v] of Object.entries(kfs[kfs.length - 1]!.properties)) {
             inheritedProps[k] = v;
@@ -2717,7 +2721,7 @@ export function convertToKeyframesInScript(
   if (!loc) return script;
 
   const anim = loc.target.animation;
-  if (anim.keyframes) return script;
+  if (authorsKeyframes(anim)) return script;
 
   const { fromProps, toProps } = resolveConversionProps(anim, resolvedFromValues);
   const varsArg = loc.target.call.varsArg;
@@ -3266,6 +3270,7 @@ export function splitIntoPropertyGroups(
   if (!loc) return { script, ids: [animationId] };
 
   const anim = loc.target.animation;
+  if (anim.hasUnresolvedKeyframes) return { script, ids: [animationId] };
 
   // Collect the properties to partition. For keyframed tweens, gather the
   // union of all properties across all keyframes. For flat tweens, use the

packages/parsers/src/gsapParserAcorn.ts

@@ -1005,7 +1005,7 @@ function parsePercentageKeyframes(
   node: any,
   scope: ScopeBindings,
   source: string,
-): GsapKeyframesData {
+): GsapKeyframesData | undefined {
   const keyframes: GsapPercentageKeyframe[] = [];
   let ease: string | undefined;
   let easeEach: string | undefined;
@@ -1017,6 +1017,7 @@ function parsePercentageKeyframes(
 
     const pctMatch = PERCENTAGE_KEY_RE.exec(key);
     if (pctMatch) {
+      if (!isPlainStep(prop.value)) return undefined;
       const percentage = Number.parseFloat(pctMatch[1] ?? "0");
       const record = objectExpressionToRecord(prop.value, scope, source);
       const properties: Record<string, number | string> = {};
@@ -1041,6 +1042,8 @@ function parsePercentageKeyframes(
       ease = tryResolveStringProp(prop.value, scope, source) ?? ease;
     } else if (key === "easeEach") {
       easeEach = tryResolveStringProp(prop.value, scope, source) ?? easeEach;
+    } else {
+      return undefined;
     }
   }
 
@@ -1073,8 +1076,20 @@ function computeKeyframesTotalDuration(
   return getObjectArrayKeyframeTiming(durations)?.totalDuration;
 }
 
-const isFullyReadableStep = (el: any) =>
-  el?.type === "ObjectExpression" && !el.properties.some((p: any) => p.type === "SpreadElement");
+function staticKeyName(prop: any): string | undefined {
+  if (prop.type !== "ObjectProperty" && prop.type !== "Property") return undefined;
+  if (prop.method || (prop.kind && prop.kind !== "init")) return undefined;
+  const key = prop.computed
+    ? prop.key?.type === "Literal" && prop.key.value
+    : (prop.key?.name ?? prop.key?.value);
+  return typeof key === "string" ? key : undefined;
+}
+
+const isPlainObject = (node: any) =>
+  node?.type === "ObjectExpression" &&
+  (node.properties ?? []).every((p: any) => staticKeyName(p) !== undefined);
+
+const isPlainStep = (node: any) => node?.type === "Literal" || isPlainObject(node);
 
 // fallow-ignore-next-line complexity
 function parseObjectArrayKeyframes(
@@ -1090,7 +1105,7 @@ function parseObjectArrayKeyframes(
   }> = [];
 
   for (const el of elements) {
-    if (!isFullyReadableStep(el)) return undefined;
+    if (!isPlainObject(el)) return undefined;
     const record = objectExpressionToRecord(el, scope, source);
     const properties: Record<string, number | string> = {};
     let duration: unknown;
@@ -1122,7 +1137,7 @@ function parseObjectArrayKeyframes(
 }
 
 // fallow-ignore-next-line complexity
-function parseSimpleArrayKeyframes(node: any, scope: ScopeBindings): GsapKeyframesData {
+function parseSimpleArrayKeyframes(node: any, scope: ScopeBindings): GsapKeyframesData | undefined {
   const arrayProps: Map<string, (number | string)[]> = new Map();
   let ease: string | undefined;
   let easeEach: string | undefined;
@@ -1136,9 +1151,8 @@ function parseSimpleArrayKeyframes(node: any, scope: ScopeBindings): GsapKeyfram
       const values: (number | string)[] = [];
       for (const el of prop.value.elements ?? []) {
         const val = resolveNode(el, scope);
-        if (typeof val === "number" || typeof val === "string") {
-          values.push(val);
-        }
+        if (typeof val !== "number" && typeof val !== "string") return undefined;
+        values.push(val);
       }
       if (values.length > 0) arrayProps.set(key, values);
     } else if (key === "ease") {
@@ -1183,6 +1197,7 @@ function parseKeyframesNode(
   if (node.type !== "ObjectExpression") return undefined;
 
   const props = node.properties ?? [];
+  if (!props.every((p: any) => staticKeyName(p) !== undefined)) return undefined;
   let hasPercentageKey = false;
   let hasArrayValue = false;
 

packages/parsers/src/gsapSerialize.ts

@@ -47,6 +47,10 @@ export function editabilityForProvenance(provenance?: GsapProvenance): KeyframeE
   return "unroll";
 }
 
+export function authorsKeyframes(anim: GsapAnimation): boolean {
+  return anim.keyframes !== undefined || anim.hasUnresolvedKeyframes === true;
+}
+
 export interface GsapAnimation {
   id: string;
   targetSelector: string;

packages/parsers/src/gsapUnroll.test.ts

@@ -228,6 +228,13 @@ fade("#a", 1);`;
     expect(unrollComputedTimeline(script)).toBe(script);
   });
 
+  it("leaves a loop as authored when a tween's keyframes cannot be read", () => {
+    const script = `const tl = gsap.timeline();
+for (let i = 0; i < 2; i++) { tl.to("#x", { duration: 1, keyframes: [{ x: 0 }, { x: 100, runBackwards: true }] }, i); }`;
+    expect(parseGsapScriptAcorn(script).animations[0]!.hasUnresolvedKeyframes).toBe(true);
+    expect(unrollComputedTimeline(script)).toBe(script);
+  });
+
   it("leaves a loop as authored when its body sets state outside the timeline", () => {
     const script = `const tl = gsap.timeline();
 for (let i = 0; i < 2; i++) { gsap.set("#x", { opacity: 0 }); tl.to("#x", { opacity: 1, duration: 1 }, i); }`;

packages/parsers/src/gsapUnroll.ts

@@ -227,14 +227,18 @@ function declaredFunctions(stmt: Node): Array<[string, Node[]]> {
 const collectHelperBodies = (statements: Node[]): Map<string, Node[]> =>
   new Map(statements.flatMap(declaredFunctions));
 
-/** Statements stay as authored when literal tweens cannot encode their timing, or they do more than add tweens. */
+/** Left as authored when literal tweens can't encode the timing or keyframes, or it does more than add tweens. */
 function dropStatementsUnsafeToUnroll(
   byStatement: Map<Node, GsapAnimation[]>,
   ctx: UnrollScope,
 ): void {
   for (const [stmt, anims] of byStatement) {
     const unknownTiming = anims.some(
-      (a) => a.durationUnresolved || a.resolvedStart === undefined || a.hasUnresolvedSelector,
+      (a) =>
+        a.durationUnresolved ||
+        a.resolvedStart === undefined ||
+        a.hasUnresolvedSelector ||
+        a.hasUnresolvedKeyframes,
     );
     const bodyStmts = unknownTiming ? null : bodyOf(stmt, ctx.helpers);
     if (bodyStmts === null || !onlyAddsTweens(bodyStmts, ctx)) byStatement.delete(stmt);

packages/parsers/src/gsapWriter.parity.test.ts

@@ -18,6 +18,7 @@ import {
   materializeKeyframesInScript as materializeRecast,
   splitIntoPropertyGroups as splitGroupsRecast,
   splitAnimationsInScript as splitAnimsRecast,
+  updateAnimationInScript as updateAnimRecast,
   setArcPathInScript as setArcRecast,
   updateArcSegmentInScript as updateArcSegmentRecast,
   removeArcPathFromScript as removeArcRecast,
@@ -55,6 +56,7 @@ import {
   resizeKeyframedTweenInScript as resizeKeyframedTweenAcorn,
   addAnimationWithKeyframesToScript as addWithKfAcorn,
   removeAnimationFromScript as removeAnimAcorn,
+  updateAnimationInScript as updateAnimAcorn,
   shiftPositionsInScript as shiftAcorn,
   scalePositionsInScript as scaleAcorn,
   retimeClipTweensInScript,
@@ -570,6 +572,150 @@ describe("parity: splitAnimationsInScript (recast vs acorn)", () => {
   });
 });
 
+describe("splitAnimationsInScript keeps keyframes the parser cannot read", () => {
+  const STEP_SHAPES = [
+    ["a step with a flag", "", "[{ x: 0 }, { x: 100, runBackwards: true }]"],
+    ["a spread step", "const base = { x: 0 };", "[{ ...base }, { x: 100 }]"],
+    ["a named step", "const last = { x: 100 };", "[{ x: 0 }, last]"],
+    ["keyframes from a call", "", "steps()"],
+  ] as const;
+  const opts = { originalId: "a", newId: "a-2", elementStart: 0, elementDuration: 4 };
+  const writers = [
+    ["recast", splitAnimsRecast],
+    ["acorn", splitAnimsAcorn],
+  ] as const;
+
+  for (const [writer, split] of writers) {
+    for (const [shape, decl, keyframes] of STEP_SHAPES) {
+      const script = `const tl = gsap.timeline({ paused: true });
+${decl}
+tl.to("#a", { duration: 2, keyframes: ${keyframes} }, 0);`;
+
+      it(`${writer}: leaves ${shape} spanning the split as authored`, () => {
+        expect(parseGsapScriptAcorn(script).animations[0]!.hasUnresolvedKeyframes).toBe(true);
+        const result = split(script, { ...opts, splitTime: 1 });
+        expect(result.script).toContain(`tl.to("#a", { duration: 2, keyframes: ${keyframes} }, 0)`);
+        expect(result.skippedSelectors).toContain("#a (keyframes spanning split)");
+      });
+
+      it(`${writer}: moves ${shape} after the split whole`, () => {
+        const result = split(script, { ...opts, splitTime: 0 });
+        expect(result.script).toContain(
+          `tl.to("#a-2", { duration: 2, keyframes: ${keyframes} }, 0)`,
+        );
+      });
+    }
+  }
+});
+
+describe("writers leave keyframes they cannot read as authored", () => {
+  const UNREADABLE = [
+    ["a step with a flag", "[{ x: 0 }, { x: 100, runBackwards: true }]"],
+    ["keyframes from a call", "steps()"],
+  ] as const;
+  const opts = { originalId: "a", newId: "a-2", elementStart: 0, elementDuration: 4 };
+
+  for (const [shape, keyframes] of UNREADABLE) {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#a", { opacity: 1, x: 5, duration: 1, keyframes: ${keyframes} }, 0);`;
+    const id = () => acornId(script);
+
+    for (const [writer, split] of [
+      ["recast", splitAnimsRecast],
+      ["acorn", splitAnimsAcorn],
+    ] as const) {
+      if (writer === "recast" && keyframes !== "steps()") continue;
+      it(`${writer}: a split after ${shape} reports that the new clip's start is unknown`, () => {
+        const result = split(`${script}\ntl.to("#a", { duration: 2, x: 200 }, 1);`, {
+          ...opts,
+          splitTime: 2,
+        });
+        expect(result.skippedSelectors).toContain("#a (unreadable keyframes before split)");
+      });
+    }
+
+    it.each([
+      ["recast convert to keyframes", () => convertRecast(script, id())],
+      ["acorn convert to keyframes", () => convertAcorn(script, id())],
+      ["recast split into property groups", () => splitGroupsRecast(script, id()).script],
+      ["acorn split into property groups", () => splitGroupsAcorn(script, id()).script],
+      ["acorn add keyframe", () => addKeyframeAcorn(script, id(), 50, { x: 10 })],
+      ["acorn update keyframe", () => updateKeyframeAcorn(script, id(), 100, { x: 10 })],
+      ["acorn remove keyframe", () => removeKeyframeAcorn(script, id(), 100)],
+      ["acorn move keyframe", () => moveKeyframeAcorn(script, id(), 100, 80)],
+      ["acorn resize keyframed tween", () => resizeKeyframedTweenAcorn(script, id(), 0, 2, [])],
+      [
+        "acorn property edit",
+        () => updateAnimAcorn(script, id(), { properties: { opacity: 0.5 } }),
+      ],
+    ])(`%s leaves ${shape} unchanged`, (_name, write) => {
+      expect(parseGsapScriptAcorn(script).animations[0]!.hasUnresolvedKeyframes).toBe(true);
+      expect(write()).toBe(script);
+    });
+  }
+
+  it.each(["{ x: v }", "{ [v]: { x: 1 } }", "{ ...o }"])(
+    "acorn add and resize leave object keyframes %s unchanged",
+    (keyframes) => {
+      const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#a", { duration: 1, keyframes: ${keyframes} }, 0);`;
+      expect(parseGsapScriptAcorn(script).animations[0]!.hasUnresolvedKeyframes).toBe(true);
+      expect(addKeyframeAcorn(script, acornId(script), 50, { x: 5 })).toBe(script);
+      expect(resizeKeyframedTweenAcorn(script, acornId(script), 0, 2, [])).toBe(script);
+    },
+  );
+
+  it.each([
+    ["recast", splitAnimsRecast],
+    ["acorn", splitAnimsAcorn],
+  ] as const)("%s: a split across unreadable keyframes writes no start value", (_writer, split) => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#a", { opacity: 0.5, duration: 2, keyframes: steps() }, 0);`;
+    const result = split(script, { ...opts, splitTime: 1 });
+    expect(result.script).not.toContain('"#a-2"');
+    expect(result.skippedSelectors).toContain("#a (keyframes spanning split)");
+  });
+
+  it("treats keyframes with a computed percentage key as unreadable", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#a", { duration: 1, keyframes: { [k]: { x: 10 }, "100%": { x: 50 } } }, 0);`;
+    const id = acornId(script);
+    expect(parseGsapScriptAcorn(script).animations[0]!.hasUnresolvedKeyframes).toBe(true);
+    expect(updateAnimAcorn(script, id, { properties: { opacity: 0.5 } })).toBe(script);
+    expect(removeKeyframeAcorn(script, id, 100)).toBe(script);
+  });
+
+  it.each([
+    ["a named step", '{ "0%": { x: 0 }, "100%": last }'],
+    ["a spread inside a step", '{ "0%": { x: 0 }, "100%": { ...base, x: 10 } }'],
+    ["a numeric key", '{ "0%": { x: 0 }, [50]: { x: 5 }, "100%": { x: 10 } }'],
+    ["a template key in an array step", "[{ x: 0 }, { x: 10, [`y`]: 5 }]"],
+    ["a variable key in an array step", "[{ x: 0 }, { x: 10, [k]: 5 }]"],
+    ["a getter in a step", '{ "0%": { x: 0 }, "100%": { get x() { return 10; } } }'],
+    ["a method in an array step", "[{ x: 0 }, { x: 10, y() {} }]"],
+    ["an array channel beside % steps", '{ "0%": { x: 0 }, "100%": { x: 10 }, y: [0, 5] }'],
+    ["an unresolved array value", "{ x: [0, 10, v] }"],
+    ["a spread in an array channel", "{ x: [0, ...rest] }"],
+    ["a hole in an array channel", "{ x: [0, , 10] }"],
+  ])(
+    "treats keyframes with %s as unreadable, so drags and deletes keep them",
+    (_shape, keyframes) => {
+      const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#a", { duration: 2, keyframes: ${keyframes} }, 0);`;
+      const id = acornId(script);
+      expect(parseGsapScriptAcorn(script).animations[0]!.hasUnresolvedKeyframes).toBe(true);
+      expect(moveKeyframeAcorn(script, id, 100, 80)).toBe(script);
+      expect(removeKeyframeAcorn(script, id, 0)).toBe(script);
+    },
+  );
+
+  it("recast property edit leaves keyframes from a call unchanged", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#a", { x: 5, duration: 1, keyframes: steps() }, 0);`;
+    expect(updateAnimRecast(script, acornId(script), { properties: { x: 9 } })).toBe(script);
+  });
+});
+
 // ─── arc path parity ──────────────────────────────────────────────────────────
 
 const ARC_FLAT_SCRIPT = `

packages/parsers/src/gsapWriterAcorn.ts

@@ -14,6 +14,7 @@ import type {
   ArcPathSegment,
 } from "./gsapSerialize.js";
 import {
+  authorsKeyframes,
   resolveConversionProps,
   extractArcWaypoints,
   buildMotionPathObjectCode,
@@ -329,7 +330,7 @@ export function updateAnimationInScript(
   const parsed = parseGsapScriptAcornForWrite(script);
   if (!parsed) return script;
   const target = parsed.located.find((l) => l.id === animationId);
-  if (!target) return script;
+  if (!target || (updates.properties && target.animation.hasUnresolvedKeyframes)) return script;
 
   const ms = new MagicString(script);
   const { call }: { call: TweenCallInfo } = target;
@@ -1078,7 +1079,7 @@ export function updateKeyframeInScript(
   const parsed = parseGsapScriptAcornForWrite(script);
   if (!parsed) return script;
   const target = parsed.located.find((l) => l.id === animationId);
-  if (!target) return script;
+  if (!target || target.animation.hasUnresolvedKeyframes) return script;
 
   const kfPropNode = findPropertyNode(target.call.varsArg, "keyframes");
   if (!kfPropNode) {
@@ -1198,7 +1199,7 @@ function locateWithKeyframes(
   const target =
     parsed.located.find((l) => l.id === animationId) ??
     parsed.located.find((l) => l.id === convertedId);
-  if (!target) return null;
+  if (!target || target.animation.hasUnresolvedKeyframes) return null;
   const kfPropNode = findPropertyNode(target.call.varsArg, "keyframes");
   if (!kfPropNode || kfPropNode.value?.type !== "ObjectExpression") return null;
   return { script, parsed, target, kfNode: kfPropNode.value };
@@ -1246,7 +1247,7 @@ function ensureKeyframesNode(
 
   const parsed = parseGsapScriptAcornForWrite(script);
   const target = parsed?.located.find((l) => l.id === animationId);
-  if (!target) return null;
+  if (!target || target.animation.hasUnresolvedKeyframes) return null;
 
   // Array-form keyframes → normalize to object form, then re-locate.
   const kfProp = findPropertyNode(target.call.varsArg, "keyframes");
@@ -1422,7 +1423,7 @@ export function removeKeyframeFromScript(
   const parsed = parseGsapScriptAcornForWrite(script);
   if (!parsed) return script;
   const target = parsed.located.find((l) => l.id === animationId);
-  if (!target) return script;
+  if (!target || target.animation.hasUnresolvedKeyframes) return script;
 
   const kfPropNode = findPropertyNode(target.call.varsArg, "keyframes");
   if (!kfPropNode) return script;
@@ -1691,7 +1692,7 @@ export function convertToKeyframesFromScript(
   const target = parsed.located.find((l) => l.id === animationId);
   if (!target) return script;
   const { animation, call } = target;
-  if (animation.keyframes) return script;
+  if (authorsKeyframes(animation)) return script;
   const isSet = call.method === "set";
 
   const { fromProps, toProps } = resolveConversionProps(animation, resolvedFromValues);
@@ -2028,6 +2029,7 @@ export function splitIntoPropertyGroupsFromScript(
   const target = parsed.located.find((l) => l.id === animationId);
   if (!target) return { script, ids: [animationId] };
   const { animation } = target;
+  if (animation.hasUnresolvedKeyframes) return { script, ids: [animationId] };
 
   const allPropKeys = collectPropertyKeys(animation);
   const groupProps = partitionPropertyGroups(allPropKeys);
@@ -2527,8 +2529,8 @@ function computeForwardBaselines(
     const dur = anim.duration ?? 0;
     const animEnd = pos + dur;
 
-    if (anim.keyframes) {
-      const kfs = anim.keyframes.keyframes;
+    if (authorsKeyframes(anim)) {
+      const kfs = anim.keyframes?.keyframes ?? [];
       if (pos >= splitTime) {
         // Moves wholly to the new element — contributes nothing to the baseline.
       } else if (animEnd > splitTime) {
@@ -2613,6 +2615,24 @@ type SplitCtx = {
   newElementStart: number;
 };
 
+function applyKeyframedTweenSplit(
+  result: string,
+  anim: GsapAnimation,
+  pos: number,
+  animEnd: number,
+  ctx: SplitCtx,
+  skippedSelectors: string[],
+): string {
+  if (pos >= ctx.splitTime)
+    return updateAnimationSelectorInScript(result, anim.id, ctx.newSelector);
+  if (animEnd > ctx.splitTime) {
+    skippedSelectors.push(`${ctx.originalSelector} (keyframes spanning split)`);
+  } else if (anim.hasUnresolvedKeyframes) {
+    skippedSelectors.push(`${ctx.originalSelector} (unreadable keyframes before split)`);
+  }
+  return result;
+}
+
 // Decide what one matching tween does at the split point: move to the new
 // element (wholly after), stay (wholly before / keyframes before), get skipped
 // (keyframes spanning), or get interpolated in half (spanning). Returns the
@@ -2628,14 +2648,8 @@ function applyTweenSplit(
   const dur = anim.duration ?? 0;
   const animEnd = pos + dur;
 
-  if (anim.keyframes) {
-    if (pos >= ctx.splitTime)
-      return updateAnimationSelectorInScript(result, anim.id, ctx.newSelector);
-    if (animEnd > ctx.splitTime) {
-      skippedSelectors.push(`${ctx.originalSelector} (keyframes spanning split)`);
-    }
-    // Inherited-state for kf tweens is handled by computeForwardBaselines.
-    return result;
+  if (authorsKeyframes(anim)) {
+    return applyKeyframedTweenSplit(result, anim, pos, animEnd, ctx, skippedSelectors);
   }
   // Wholly before the split — kept on the original element.
   if (animEnd <= ctx.splitTime) return result;