marko-js · DylanPiercey · Jul 10, 2026
diff --git a/.changeset/for-branch-list-owners.md b/.changeset/for-branch-list-owners.md
@@ -0,0 +1,5 @@
+---
+"@marko/runtime-tags": patch
+---
+
+Link `<for>` branch owners from the parent's serialized branch list instead of serializing `_` per iteration: the list serializes through an owner-assigning wrapper (`_.o`), and the per-branch owner prop is elided when markers are statically off, or guarded by the marker condition when it is runtime-dependent.
diff --git a/.sizes.json b/.sizes.json
@@ -7,8 +7,8 @@
     {
       "name": "*",
       "total": {
-        "min": 25857,
-        "brotli": 9518
+        "min": 25909,
+        "brotli": 9529
       }
     },
     {
@@ -33,12 +33,12 @@
         "brotli": 80
       },
       "runtime": {
-        "min": 2463,
-        "brotli": 1239
+        "min": 2585,
+        "brotli": 1279
       },
       "total": {
-        "min": 2543,
-        "brotli": 1319
+        "min": 2665,
+        "brotli": 1359
       }
     },
     {
@@ -63,12 +63,12 @@
         "brotli": 101
       },
       "runtime": {
-        "min": 2668,
-        "brotli": 1309
+        "min": 2790,
+        "brotli": 1352
       },
       "total": {
-        "min": 2783,
-        "brotli": 1410
+        "min": 2905,
+        "brotli": 1453
       }
     }
   ]

diff --git a/.sizes/comments.ssr/runtime.js b/.sizes/comments.ssr/runtime.js
@@ -1,4 +1,4 @@
-// size: 2668 (min) 1309 (brotli)
+// size: 2790 (min) 1352 (brotli)
 //#region packages/runtime-tags/dist/dom.mjs
 let decodeAccessor = (num) =>
     (num + (num < 26 ? 10 : num < 962 ? 334 : 11998)).toString(36),
@@ -21,6 +21,11 @@ let decodeAccessor = (num) =>
 function isNotVoid(value) {
   return value != null && value !== !1;
 }
+function forEach(opt, cb) {
+  if (opt)
+    if (Array.isArray(opt)) for (let item of opt) cb(item);
+    else cb(opt);
+}
 function _on(element, type, handler) {
   (element["$" + type] === void 0 && delegate(type, handleDelegated),
     (element["$" + type] = handler || null));
@@ -146,6 +151,15 @@ function init(runtimeId = "M") {
             lastTokenIndex;
           return (
             (serializeContext._ = registeredValues),
+            (serializeContext.o = (ownerId, scopes) => {
+              let owner = getScope(ownerId);
+              return (
+                forEach(scopes, (scope) => {
+                  scope._ ??= owner;
+                }),
+                scopes
+              );
+            }),
             (render.m = (effects) => {
               if ((processResumes(render.r, effects), readyIds));
               let retained = 0;

diff --git a/.sizes/counter.ssr/runtime.js b/.sizes/counter.ssr/runtime.js
@@ -1,4 +1,4 @@
-// size: 2463 (min) 1239 (brotli)
+// size: 2585 (min) 1279 (brotli)
 //#region packages/runtime-tags/dist/dom.mjs
 let decodeAccessor = (num) =>
     (num + (num < 26 ? 10 : num < 962 ? 334 : 11998)).toString(36),
@@ -18,6 +18,11 @@ let decodeAccessor = (num) =>
   },
   runRender = (render) => render.c(render.b, render.d),
   catchEnabled;
+function forEach(opt, cb) {
+  if (opt)
+    if (Array.isArray(opt)) for (let item of opt) cb(item);
+    else cb(opt);
+}
 function _on(element, type, handler) {
   (element["$" + type] === void 0 && delegate(type, handleDelegated),
     (element["$" + type] = handler || null));
@@ -143,6 +148,15 @@ function init(runtimeId = "M") {
             lastTokenIndex;
           return (
             (serializeContext._ = registeredValues),
+            (serializeContext.o = (ownerId, scopes) => {
+              let owner = getScope(ownerId);
+              return (
+                forEach(scopes, (scope) => {
+                  scope._ ??= owner;
+                }),
+                scopes
+              );
+            }),
             (render.m = (effects) => {
               if ((processResumes(render.r, effects), readyIds));
               let retained = 0;

diff --git a/.sizes/dom.js b/.sizes/dom.js
@@ -1,4 +1,4 @@
-// size: 25857 (min) 9518 (brotli)
+// size: 25909 (min) 9529 (brotli)
 //#region packages/runtime-tags/dist/dom.mjs
 let empty = [],
   rest = Symbol(),
@@ -1038,6 +1038,15 @@ function init(runtimeId = "M") {
             embedAnchor;
           return (
             (serializeContext._ = registeredValues),
+            (serializeContext.o = (ownerId, scopes) => {
+              let owner = getScope(ownerId);
+              return (
+                forEach(scopes, (scope) => {
+                  scope._ ??= owner;
+                }),
+                scopes
+              );
+            }),
             (render.m = (effects) => {
               if ((processResumes(render.r, effects), readyIds && render.b))
                 for (let progress = 1; progress;) {

diff --git a/packages/runtime-tags/src/__tests__/fixtures-interop/interop-basic-tags-to-class/sizes.json b/packages/runtime-tags/src/__tests__/fixtures-interop/interop-basic-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67437,
-        "brotli": 20862
+        "min": 67488,
+        "brotli": 20851
       },
       "files": {
         "components/class-counter.marko": 1028,

diff --git a/.../runtime-tags/src/__tests__/fixtures-interop/interop-basic-tags-to-inert-class/sizes.json b/.../runtime-tags/src/__tests__/fixtures-interop/interop-basic-tags-to-inert-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 3160,
-        "brotli": 1544
+        "min": 3282,
+        "brotli": 1590
       },
       "files": {
         "template.marko": 236,

diff --git a/.../runtime-tags/src/__tests__/fixtures-interop/interop-emit-inline-tags-to-class/sizes.json b/.../runtime-tags/src/__tests__/fixtures-interop/interop-emit-inline-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67429,
-        "brotli": 20817
+        "min": 67480,
+        "brotli": 20840
       },
       "files": {
         "components/inline-button.marko": 1094,

diff --git a/...s/runtime-tags/src/__tests__/fixtures-interop/interop-emit-split-tags-to-class/sizes.json b/...s/runtime-tags/src/__tests__/fixtures-interop/interop-emit-split-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67548,
-        "brotli": 20902
+        "min": 67599,
+        "brotli": 20885
       },
       "files": {
         "components/split-button/component-browser.js": 373,

diff --git a/...src/__tests__/fixtures-interop/interop-event-handler-render-body-tags-to-class/sizes.json b/...src/__tests__/fixtures-interop/interop-event-handler-render-body-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67737,
-        "brotli": 21009
+        "min": 67788,
+        "brotli": 21065
       },
       "files": {
         "components/my-button.marko": 1048,

diff --git a/packages/runtime-tags/src/__tests__/fixtures-interop/interop-events-tags-to-class/sizes.json b/packages/runtime-tags/src/__tests__/fixtures-interop/interop-events-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67371,
-        "brotli": 20782
+        "min": 67422,
+        "brotli": 20802
       },
       "files": {
         "components/class-counter.marko": 1043,

diff --git a/.../src/__tests__/fixtures-interop/interop-mixed-inert-and-stateful-tags-to-class/sizes.json b/.../src/__tests__/fixtures-interop/interop-mixed-inert-and-stateful-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67437,
-        "brotli": 20867
+        "min": 67488,
+        "brotli": 20862
       },
       "files": {
         "components/class-counter.marko": 1028,

diff --git a/packages/runtime-tags/src/__tests__/fixtures-interop/interop-nested-tags-to-class/sizes.json b/packages/runtime-tags/src/__tests__/fixtures-interop/interop-nested-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67882,
-        "brotli": 21060
+        "min": 67933,
+        "brotli": 21041
       },
       "files": {
         "components/class-layout.marko": 1227,

diff --git a/...ntime-tags/src/__tests__/fixtures-interop/interop-reactive-split-tags-to-class/sizes.json b/...ntime-tags/src/__tests__/fixtures-interop/interop-reactive-split-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67379,
-        "brotli": 20851
+        "min": 67430,
+        "brotli": 20907
       },
       "files": {
         "components/split-display/component-browser.js": 182,

diff --git a/packages/runtime-tags/src/__tests__/fixtures-interop/interop-rerender-inert-class/sizes.json b/packages/runtime-tags/src/__tests__/fixtures-interop/interop-rerender-inert-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67049,
-        "brotli": 20714
+        "min": 67100,
+        "brotli": 20771
       },
       "files": {
         "components/class-display.marko": 856,

diff --git a/...time-tags/src/__tests__/fixtures-interop/interop-roundtrip-split-tags-to-class/sizes.json b/...time-tags/src/__tests__/fixtures-interop/interop-roundtrip-split-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67545,
-        "brotli": 20905
+        "min": 67596,
+        "brotli": 20874
       },
       "files": {
         "components/split-counter/component-browser.js": 228,

diff --git a/...es/runtime-tags/src/__tests__/fixtures-interop/interop-stateless-tags-to-class/sizes.json b/...es/runtime-tags/src/__tests__/fixtures-interop/interop-stateless-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 67152,
-        "brotli": 20719
+        "min": 67203,
+        "brotli": 20712
       },
       "files": {
         "components/my-button/component-browser.js": 457,

diff --git a/...s/runtime-tags/src/__tests__/fixtures-interop/interop-tag-params-tags-to-class/sizes.json b/...s/runtime-tags/src/__tests__/fixtures-interop/interop-tag-params-tags-to-class/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 68241,
-        "brotli": 21215
+        "min": 68292,
+        "brotli": 21248
       },
       "files": {
         "components/class-layout.marko": 1245,

diff --git a/packages/runtime-tags/src/__tests__/fixtures-interop/let/sizes.json b/packages/runtime-tags/src/__tests__/fixtures-interop/let/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 3150,
-      "brotli": 1540
+      "min": 3272,
+      "brotli": 1586
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/abort-signal-deduped/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/abort-signal-deduped/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 1791,
-      "brotli": 941
+      "min": 1913,
+      "brotli": 984
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-derived-to-undefined/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-derived-to-undefined/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2739,
-      "brotli": 1367
+      "min": 2861,
+      "brotli": 1421
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-destructured-increment/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-destructured-increment/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2841,
-      "brotli": 1417
+      "min": 2963,
+      "brotli": 1467
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-destructured-reduced/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-destructured-reduced/sizes.json
@@ -2,8 +2,8 @@
   "dom": {
     "template.marko.page.mjs": {
       "total": {
-        "min": 2544,
-        "brotli": 1290
+        "min": 2666,
+        "brotli": 1324
       },
       "files": {
         "tags/child.marko": 323,

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-destructured/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-destructured/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2655,
-      "brotli": 1334
+      "min": 2777,
+      "brotli": 1391
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-in-wrapped-function/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-in-wrapped-function/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2633,
-      "brotli": 1331
+      "min": 2755,
+      "brotli": 1379
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-let-to-undefined/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-let-to-undefined/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2636,
-      "brotli": 1341
+      "min": 2758,
+      "brotli": 1386
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-live-read/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-live-read/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2823,
-      "brotli": 1396
+      "min": 2945,
+      "brotli": 1447
     }
   },
   "html": {

diff --git a/packages/runtime-tags/src/__tests__/fixtures/assign-multiple-derived-chain/sizes.json b/packages/runtime-tags/src/__tests__/fixtures/assign-multiple-derived-chain/sizes.json
@@ -1,8 +1,8 @@
 {
   "dom": {
     "template.marko.page.mjs": {
-      "min": 2974,
-      "brotli": 1478
+      "min": 3096,
+      "brotli": 1540
     }
   },
   "html": {