diff --git a/src/plugins/inspectorViews/elements/ElementItem.vue b/src/plugins/inspectorViews/elements/ElementItem.vue
index f668f6b8b2..e2770b1646 100644
--- a/src/plugins/inspectorViews/elements/ElementItem.vue
+++ b/src/plugins/inspectorViews/elements/ElementItem.vue
@@ -45,6 +45,7 @@
         :object-path="[elementObject, domainObject]"
         @context-click-active="setContextClickState"
       />
+      <slot name="content"></slot>
     </div>
   </li>
 </template>
diff --git a/src/plugins/inspectorViews/elements/ElementsPool.vue b/src/plugins/inspectorViews/elements/ElementsPool.vue
index 06ee6de757..b465c9cbf0 100644
--- a/src/plugins/inspectorViews/elements/ElementsPool.vue
+++ b/src/plugins/inspectorViews/elements/ElementsPool.vue
@@ -42,7 +42,11 @@
           :allow-drop="allowDrop"
           @dragstart-custom="moveFrom(index)"
           @drop-custom="moveTo(index)"
-        />
+        >
+          <template #content="slotProps">
+            <slot name="content" :index="index" :object="element" v-bind="slotProps"></slot>
+          </template>
+        </ElementItem>
         <li class="js-last-place" @drop="moveToIndex(elements.length)"></li>
       </ul>
       <div v-if="elements.length === 0">No contained elements</div>
diff --git a/src/plugins/inspectorViews/elements/ElementsViewProvider.js b/src/plugins/inspectorViews/elements/ElementsViewProvider.js
index ce9748861a..dc66f3a3b1 100644
--- a/src/plugins/inspectorViews/elements/ElementsViewProvider.js
+++ b/src/plugins/inspectorViews/elements/ElementsViewProvider.js
@@ -29,6 +29,7 @@ export default function ElementsViewProvider(openmct) {
     key: 'elementsView',
     name: 'Elements',
     canView: function (selection) {
+      // TODO - only use this view provider if another custom provider has not been applied
       const hasValidSelection = selection?.length;
       const isOverlayPlot = selection?.[0]?.[0]?.context?.item?.type === 'telemetry.plot.overlay';
 
diff --git a/src/plugins/timeline/Container.js b/src/plugins/timeline/Container.js
index 3f729d56da..8832556bdc 100644
--- a/src/plugins/timeline/Container.js
+++ b/src/plugins/timeline/Container.js
@@ -1,8 +1,52 @@
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2024, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+
+/**
+ * a sizing container for objects in a layout
+ */
 class Container {
   constructor(domainObject, size) {
+    /**
+     * the identifier of the associated domain object
+     * @type {import('@/api/objects/ObjectAPI.js').Identifier}
+     */
     this.domainObjectIdentifier = domainObject.identifier;
+    /**
+     * the size in percentage or pixels
+     * @type {number}
+     */
     this.size = size;
+    /**
+     * the default percentage scale of an object
+     * @type {number}
+     */
     this.scale = getContainerScale(domainObject);
+    /**
+     * true if the container should be a fixed pixel size
+     * false if the container should be a flexible percentage size
+     * containers are added as flex
+     * @type {boolean}
+     */
+    this.fixed = false;
   }
 }
 
diff --git a/src/plugins/timeline/TimelineElementsContent.vue b/src/plugins/timeline/TimelineElementsContent.vue
new file mode 100644
index 0000000000..4c38750e1b
--- /dev/null
+++ b/src/plugins/timeline/TimelineElementsContent.vue
@@ -0,0 +1,82 @@
+<template>
+  <template v-if="fixed">
+    <input
+      :value="size"
+      aria-labelledby="pixelSize"
+      class="field control"
+      :pattern="/\d+/"
+      type="number"
+      name="value"
+      min="0"
+      @change="changeSize"
+    />
+    <span>px</span>
+  </template>
+  <select v-model="isFixed" aria-label="fixedOrFlex">
+    <option :selected="!isFixed" :value="false">flex</option>
+    <option :selected="isFixed" :value="true">fixed</option>
+  </select>
+</template>
+<script>
+import { computed, inject, ref, toRaw } from 'vue';
+
+export default {
+  props: {
+    object: {
+      type: Object,
+      required: true
+    },
+    index: {
+      type: Number,
+      required: true
+    }
+  },
+  setup(props) {
+    const openmct = inject('openmct');
+    const domainObject = inject('domainObject');
+
+    openmct.objects.observe(domainObject, 'configuration.containers', updateContainer);
+
+    const container = ref(null);
+    const fixed = computed(() => {
+      return container.value?.fixed;
+    });
+    const isFixed = computed({ get: () => fixed, set: (_isFixed) => toggleFixed(_isFixed) });
+    const size = computed(() => container.value?.size);
+
+    function toggleFixed(_fixed) {
+      openmct.objectViews.emit(
+        `contextAction:${openmct.objects.makeKeyString(domainObject.identifier)}`,
+        'toggleFixedContextAction',
+        props.index,
+        _fixed
+      );
+    }
+
+    function changeSize(event) {
+      const _size = Number(event.target.value);
+      openmct.objectViews.emit(
+        `contextAction:${openmct.objects.makeKeyString(domainObject.identifier)}`,
+        'changeSizeContextAction',
+        props.index,
+        _size
+      );
+    }
+
+    function updateContainer(containers) {
+      container.value = containers[props.index];
+    }
+
+    return {
+      openmct,
+      domainObject,
+      container,
+      fixed,
+      isFixed,
+      size,
+      updateContainer,
+      changeSize
+    };
+  }
+};
+</script>
diff --git a/src/plugins/timeline/TimelineElementsPool.vue b/src/plugins/timeline/TimelineElementsPool.vue
new file mode 100644
index 0000000000..43c9e3df2a
--- /dev/null
+++ b/src/plugins/timeline/TimelineElementsPool.vue
@@ -0,0 +1,21 @@
+<template>
+  <ElementsPool>
+    <template #content="{ index, object }">
+      <TimelineElementsContent :index="index" :object="object" />
+    </template>
+  </ElementsPool>
+</template>
+<script>
+import ElementsPool from '@/plugins/inspectorViews/elements/ElementsPool.vue';
+
+import TimelineElementsContent from './TimelineElementsContent.vue';
+export default {
+  components: {
+    ElementsPool,
+    TimelineElementsContent
+  },
+  setup() {
+    return {};
+  }
+};
+</script>
diff --git a/src/plugins/timeline/TimelineElementsViewProvider.js b/src/plugins/timeline/TimelineElementsViewProvider.js
new file mode 100644
index 0000000000..73b5023915
--- /dev/null
+++ b/src/plugins/timeline/TimelineElementsViewProvider.js
@@ -0,0 +1,76 @@
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2024, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+
+import mount from 'utils/mount';
+
+import TimelineElementsPool from './TimelineElementsPool.vue';
+
+export default function TimelineElementsViewProvider(openmct) {
+  return {
+    key: 'timelineElementsView',
+    name: 'Elements',
+    canView: function (selection) {
+      return selection?.[0]?.[0]?.context?.item?.type === 'time-strip';
+    },
+    view: function (selection) {
+      let _destroy = null;
+
+      const domainObject = selection?.[0]?.[0]?.context?.item;
+
+      return {
+        show: function (element) {
+          const { destroy } = mount(
+            {
+              el: element,
+              components: {
+                TimelineElementsPool
+              },
+              provide: {
+                openmct,
+                domainObject
+              },
+              template: `<TimelineElementsPool />`
+            },
+            {
+              app: openmct.app,
+              element
+            }
+          );
+          _destroy = destroy;
+        },
+        showTab: function (isEditing) {
+          const hasComposition = Boolean(domainObject && openmct.composition.get(domainObject));
+
+          return hasComposition && isEditing;
+        },
+        priority: function () {
+          return openmct.priority.HIGH - 1;
+        },
+        destroy: function () {
+          if (_destroy) {
+            _destroy();
+          }
+        }
+      };
+    }
+  };
+}
diff --git a/src/plugins/timeline/TimelineObjectView.vue b/src/plugins/timeline/TimelineObjectView.vue
index 7d3db098d5..e1afbc3035 100644
--- a/src/plugins/timeline/TimelineObjectView.vue
+++ b/src/plugins/timeline/TimelineObjectView.vue
@@ -32,7 +32,8 @@
     :hide-button="!item.isEventTelemetry"
     :button-click-on="enableExtendEventLines"
     :button-click-off="disableExtendEventLines"
-    :style="[{ 'flex-basis': sizeString }]"
+    :class="sizeClass"
+    :style="sizeStyle"
   >
     <template #label>
       {{ item.domainObject.name }}
@@ -64,12 +65,12 @@ export default {
       type: Object,
       required: true
     },
-    extendedLinesBus: {
+    container: {
       type: Object,
       required: true
     },
-    size: {
-      type: Number,
+    extendedLinesBus: {
+      type: Object,
       required: true
     }
   },
@@ -81,8 +82,17 @@ export default {
     };
   },
   computed: {
-    sizeString() {
-      return `${this.size}%`;
+    size() {
+      return this.container.size;
+    },
+    fixed() {
+      return this.container.fixed;
+    },
+    sizeClass() {
+      return `--${this.fixed ? 'fixed' : 'scales'}`;
+    },
+    sizeStyle() {
+      return `flex-basis: ${this.size}${this.fixed ? 'px' : '%'}`;
     }
   },
   watch: {
diff --git a/src/plugins/timeline/TimelineViewLayout.vue b/src/plugins/timeline/TimelineViewLayout.vue
index b1ccf20de4..1b8382bb32 100644
--- a/src/plugins/timeline/TimelineViewLayout.vue
+++ b/src/plugins/timeline/TimelineViewLayout.vue
@@ -47,7 +47,7 @@
         <TimelineObjectView
           class="c-timeline__content js-timeline__content"
           :item="item"
-          :size="getContainerSize(item)"
+          :container="containers[index]"
           :extended-lines-bus
         />
         <ResizeHandle
@@ -76,7 +76,7 @@
 import _ from 'lodash';
 import { useDragResizer } from 'utils/vue/useDragResizer.js';
 import { useFlexContainers } from 'utils/vue/useFlexContainers.js';
-import { inject, onBeforeUnmount, onMounted, provide, ref } from 'vue';
+import { inject, onBeforeUnmount, provide, ref, toRaw } from 'vue';
 
 import SwimLane from '@/ui/components/swim-lane/SwimLane.vue';
 import ResizeHandle from '@/ui/layout/ResizeHandle/ResizeHandle.vue';
@@ -109,11 +109,17 @@ export default {
     const openmct = inject('openmct');
     const domainObject = inject('domainObject');
     const path = inject('path');
-    const composition = inject('composition');
     const extendedLinesBus = inject('extendedLinesBus');
 
+    const composition = ref(null);
+    let isCompositionLoaded = false;
+    const existingContainers = [];
+    const compositionCollection = openmct.composition.get(toRaw(domainObject));
+    compositionCollection.on('add', addItem);
+    compositionCollection.on('remove', removeItem);
+    compositionCollection.on('reorder', reorder);
+
     const items = ref([]);
-    const loadedComposition = ref(null);
     const extendedLinesPerKey = ref({});
 
     const { alignment: alignmentData, reset: resetAlignment } = useAlignment(
@@ -146,16 +152,56 @@ export default {
       addContainer,
       removeContainer,
       reorderContainers,
+      setContainers,
       containers,
       startContainerResizing,
       containerResizing,
-      endContainerResizing
+      endContainerResizing,
+      toggleFixed,
+      sizeFixedContainer
     } = useFlexContainers(timelineHolder, {
       containers: domainObject.configuration.containers,
       rowsLayout: true,
       callback: mutateContainers
     });
 
+    compositionCollection.load().then((loadedComposition) => {
+      composition.value = loadedComposition;
+      isCompositionLoaded = true;
+
+      // check if containers configuration matches composition
+      // in case composition has been modified outside of view
+      // if so, rebuild containers to match composition
+      // sync containers to composition,
+      // in case composition modified outside of view
+      // but do not mutate until user makes a change
+      let isConfigurationChanged = false;
+      composition.value.forEach((object, index) => {
+        const containerIndex = domainObject.configuration.containers.findIndex((container) =>
+          openmct.objects.areIdsEqual(container.domainObjectIdentifier, object.identifier)
+        );
+
+        if (containerIndex !== index) {
+          isConfigurationChanged = true;
+        }
+
+        if (containerIndex > -1) {
+          existingContainers.push(domainObject.configuration.containers[containerIndex]);
+        } else {
+          const container = new Container(object);
+          existingContainers.push(container);
+        }
+      });
+
+      // add check for total size not equal to 100? if comp and containers same, probably safe
+
+      if (isConfigurationChanged) {
+        console.log('yo');
+        setContainers(existingContainers);
+        mutateContainers();
+      }
+    });
+
     function addItem(_domainObject) {
       let rowCount = 0;
 
@@ -187,14 +233,7 @@ export default {
 
       items.value.push(item);
 
-      if (
-        !containers.value.some((container) =>
-          openmct.objects.areIdsEqual(
-            container.domainObjectIdentifier,
-            item.domainObject.identifier
-          )
-        )
-      ) {
+      if (isCompositionLoaded) {
         const container = new Container(domainObject);
         addContainer(container);
       }
@@ -245,30 +284,20 @@ export default {
       openmct.objects.mutate(domainObject, 'configuration.containers', containers.value);
     }
 
-    onMounted(async () => {
-      if (composition) {
-        composition.on('add', addItem);
-        composition.on('remove', removeItem);
-        composition.on('reorder', reorder);
+    // context action called from outside component
+    function toggleFixedContextAction(index, fixed) {
+      toggleFixed(index, fixed);
+    }
 
-        loadedComposition.value = await composition.load();
-
-        const containersToRemove = containers.value.filter(
-          (container) =>
-            !items.value.some((item) =>
-              openmct.objects.areIdsEqual(
-                container.domainObjectIdentifier,
-                item.domainObject.identifier
-              )
-            )
-        );
-      }
-    });
+    // context action called from outside component
+    function changeSizeContextAction(index, size) {
+      sizeFixedContainer(index, size);
+    }
 
     onBeforeUnmount(() => {
-      composition.off('add', addItem);
-      composition.off('remove', removeItem);
-      composition.off('reorder', reorder);
+      compositionCollection.off('add', addItem);
+      compositionCollection.off('remove', removeItem);
+      compositionCollection.off('reorder', reorder);
     });
 
     return {
@@ -281,7 +310,6 @@ export default {
       containers,
       getContainerSize,
       timelineHolder,
-      loadedComposition,
       items,
       addContainer,
       removeContainer,
@@ -291,7 +319,9 @@ export default {
       startContainerResizing,
       containerResizing,
       endContainerResizing,
-      mutateContainers
+      mutateContainers,
+      toggleFixedContextAction,
+      changeSizeContextAction
     };
   },
   data() {
diff --git a/src/plugins/timeline/TimelineViewProvider.js b/src/plugins/timeline/TimelineViewProvider.js
index b76409057f..3bb43875d3 100644
--- a/src/plugins/timeline/TimelineViewProvider.js
+++ b/src/plugins/timeline/TimelineViewProvider.js
@@ -61,7 +61,8 @@ export default function TimelineViewProvider(openmct, extendedLinesBus) {
                   isEditing
                 };
               },
-              template: '<timeline-view-layout :is-editing="isEditing"></timeline-view-layout>'
+              template:
+                '<timeline-view-layout ref="timeline" :is-editing="isEditing"></timeline-view-layout>'
             },
             {
               app: openmct.app,
@@ -71,6 +72,11 @@ export default function TimelineViewProvider(openmct, extendedLinesBus) {
           component = vNode.componentInstance;
           _destroy = destroy;
         },
+        contextAction(action, ...args) {
+          if (component?.$refs?.timeline?.[action]) {
+            component.$refs.timeline[action](...args);
+          }
+        },
         onEditModeChange(isEditing) {
           component.isEditing = isEditing;
         },
diff --git a/src/plugins/timeline/configuration.js b/src/plugins/timeline/configuration.js
index 0128f990dd..cb31653da7 100644
--- a/src/plugins/timeline/configuration.js
+++ b/src/plugins/timeline/configuration.js
@@ -1,3 +1,31 @@
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2024, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+
+/**
+ * @typedef {Object} TimeStripConfig configuration for Time Strip views
+ * @property {boolean} useIndependentTime true for independent time, false for global time
+ * @property {Array<import('./Container').default>} containers
+ * @property {number} swimLaneLabelWidth
+ */
 export const configuration = {
   useIndependentTime: false,
   containers: [],
diff --git a/src/plugins/timeline/plugin.js b/src/plugins/timeline/plugin.js
index f0fd2294f7..9704fd7234 100644
--- a/src/plugins/timeline/plugin.js
+++ b/src/plugins/timeline/plugin.js
@@ -23,9 +23,9 @@
 import { configuration } from './configuration.js';
 import ExtendedLinesBus from './ExtendedLinesBus.js';
 import TimelineCompositionPolicy from './TimelineCompositionPolicy.js';
+import TimelineElementsViewProvider from './TimelineElementsViewProvider.js';
 import timelineInterceptor from './timelineInterceptor.js';
 import TimelineViewProvider from './TimelineViewProvider.js';
-
 const extendedLinesBus = new ExtendedLinesBus();
 
 export { extendedLinesBus };
@@ -48,6 +48,7 @@ export default function () {
     openmct.composition.addPolicy(new TimelineCompositionPolicy(openmct).allow);
 
     openmct.objectViews.addProvider(new TimelineViewProvider(openmct, extendedLinesBus));
+    openmct.inspectorViews.addProvider(new TimelineElementsViewProvider(openmct));
   }
 
   install.extendedLinesBus = extendedLinesBus;
diff --git a/src/plugins/timeline/timeline.scss b/src/plugins/timeline/timeline.scss
index dc81b19676..b83c64ea32 100644
--- a/src/plugins/timeline/timeline.scss
+++ b/src/plugins/timeline/timeline.scss
@@ -45,6 +45,18 @@
     }
   }
 
+  &__content {
+    &.--scales {
+      flex-grow: 1;
+      flex-shrink: 1;
+    }
+
+    &.--fixed {
+      flex-grow: 0;
+      flex-shrink: 0;
+    }
+  }
+
   &__overlay-lines {
     @include abs();
     opacity: 0.5;
diff --git a/src/utils/vue/useFlexContainers.js b/src/utils/vue/useFlexContainers.js
index 4a949b606d..f2d68c59f2 100644
--- a/src/utils/vue/useFlexContainers.js
+++ b/src/utils/vue/useFlexContainers.js
@@ -1,5 +1,26 @@
-import _ from 'lodash';
-import { ref } from 'vue';
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2024, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+
+import { computed, ref } from 'vue';
 
 /**
  * @typedef {Object} configuration
@@ -22,25 +43,29 @@ export function useFlexContainers(
 ) {
   const containers = ref(existingContainers);
   const maxMoveSize = ref(null);
-  let sizingContainers = 0;
+
+  const fixedContainersSize = computed(() => {
+    return containers.value
+      .filter((container) => container.fixed === true)
+      .reduce((size, currentContainer) => size + currentContainer.size, 0);
+  });
 
   function addContainer(container) {
     containers.value.push(container);
 
-    if (container.scale) {
-      sizingContainers += container.scale;
-    } else {
-      sizingContainers++;
-    }
-
-    sizeItems(containers.value, container);
+    sizeItems(containers.value);
 
     callback?.();
   }
 
   function removeContainer(index) {
+    const isFlexContainer = !containers.value[index].fixed;
+
     containers.value.splice(index, 1);
-    sizeToFill(containers.value);
+
+    if (isFlexContainer) {
+      sizeItems(containers.value);
+    }
 
     callback?.();
   }
@@ -55,20 +80,44 @@ export function useFlexContainers(
     callback?.();
   }
 
-  function startContainerResizing(index) {
-    const beforeContainer = containers.value[index];
-    const afterContainer = containers.value[index + 1];
+  function setContainers(_containers) {
+    containers.value = _containers;
+    sizeItems(containers.value);
+  }
 
-    maxMoveSize.value = beforeContainer.size + afterContainer.size;
+  function startContainerResizing(index) {
+    const beforeContainer = getBeforeContainer(index);
+    const afterContainer = getAfterContainer(index);
+
+    if (beforeContainer && afterContainer && !beforeContainer.fixed && !afterContainer.fixed) {
+      maxMoveSize.value = beforeContainer.size + afterContainer.size;
+    }
+  }
+
+  function getBeforeContainer(index) {
+    return containers.value
+      .slice(0, index + 1)
+      .filter((container) => !container.fixed === true)
+      .at(-1);
+  }
+
+  function getAfterContainer(index) {
+    return containers.value.slice(index + 1).filter((container) => !container.fixed === true)[0];
   }
 
   function containerResizing(index, delta, event) {
-    let percentageMoved = Math.round((delta / getElSize()) * 100);
-    let beforeContainer = containers.value[index];
-    let afterContainer = containers.value[index + 1];
+    const beforeContainer = getBeforeContainer(index);
+    const afterContainer = getAfterContainer(index);
+    const percentageMoved = Math.round((delta / getElSize()) * 100);
 
-    beforeContainer.size = getContainerSize(beforeContainer.size + percentageMoved);
-    afterContainer.size = getContainerSize(afterContainer.size - percentageMoved);
+    if (beforeContainer && afterContainer && !beforeContainer.fixed && !afterContainer.fixed) {
+      beforeContainer.size = getContainerSize(beforeContainer.size + percentageMoved);
+      afterContainer.size = getContainerSize(afterContainer.size - percentageMoved);
+    } else {
+      console.warn(
+        'Drag requires two flexible containers. Use Elements Tab in Inspector to resize.'
+      );
+    }
   }
 
   function endContainerResizing() {
@@ -76,11 +125,9 @@ export function useFlexContainers(
   }
 
   function getElSize() {
-    if (rowsLayout) {
-      return element.value.offsetHeight;
-    } else {
-      return element.value.offsetWidth;
-    }
+    const elSize = rowsLayout === true ? element.value.offsetHeight : element.value.offsetWidth;
+
+    return elSize - fixedContainersSize.value;
   }
 
   function getContainerSize(size) {
@@ -94,69 +141,118 @@ export function useFlexContainers(
   }
 
   /**
-   * Resize items so that newItem fits proportionally (newItem must be an element of items).
-   * If newItem does not have a size or is sized at 100%,
-   * newItem will have size set to (1 * newItemScale) / n * 100,
-   * where n is the total number of items and newItemScale is the scale of newItem.
-   * All other items will be resized to fit inside the remaining space.
+   * Resize flexible sized items so they fit proportionally within a viewport
+   * 1. add size to 0 sized items based on scale proportional to total scale
+   * 2. resize item sizes to equal 100
+   * if total size < 100, resize all items
+   * if total size > 100, resize only items not resized in step 1 (newly added)
+   * 3. round excess and apply to last item
+   *
+   * Items may have a scale (ie. items with composition)
+   *
+   * Handles single add or removal, as well as atypical use cases,
+   * such as composition out of sync with containers config
+   * due to composition edits outside of view
+   *
    * @param {*} items
-   * @param {*} newItem
+   * @param {Number} (optional) index of the item to apply excess to in the event of rounding errors
    */
-  function sizeItems(items, newItem) {
-    const newItemScale = newItem.scale || 1;
+  function sizeItems(items, index) {
+    let totalSize;
+    const flexItems = items.filter((item) => !item.fixed);
+    const flexItemsWithSize = flexItems.filter((item) => item.size);
+    const flexItemsWithoutSize = flexItems.filter((item) => !item.size);
+    // total number of flexible items, adjusted by each item scale
+    const totalScale = flexItems.reduce((total, item) => {
+      const scale = item.scale ?? 1;
+      return total + scale;
+    }, 0);
 
-    if (!newItem.size && items.length === 1) {
-      newItem.size = 100;
-    } else {
-      if (!newItem.size || newItem.size === 100) {
-        newItem.size = Math.round((100 * newItemScale) / sizingContainers);
+    flexItemsWithoutSize.forEach((item) => {
+      const scale = item.scale ?? 1;
+      item.size = Math.round((100 * scale) / totalScale);
+    });
 
-        // Resize oldItems to fit inside remaining space;
-        const oldItems = items.filter((item) => !_.isEqual(item, newItem));
-        const remainingSize = 100 - newItem.size;
+    totalSize = flexItems.reduce((total, item) => total + item.size, 0);
 
-        oldItems.forEach((item) => {
-          const itemScale = item.scale || 1;
-          item.size = Math.round((item.size * itemScale * remainingSize) / 100);
-        });
+    if (totalSize > 100) {
+      const addedSize = flexItemsWithoutSize.reduce((total, item) => total + item.size, 0);
+      const remainingSize = 100 - addedSize;
 
-        // Ensure items add up to 100 in case of rounding error.
-        const total = items.reduce((t, item) => t + item.size, 0);
-        const excess = Math.round(100 - total);
-        oldItems[oldItems.length - 1].size += excess;
-      }
+      flexItemsWithSize.forEach((item) => {
+        const scale = item.scale ?? 1;
+        item.size = Math.round((item.size * scale * remainingSize) / 100);
+      });
+    } else if (totalSize < 100) {
+      const sizeToFill = 100 - totalSize;
+
+      flexItems.forEach((item) => {
+        const scale = item.scale ?? 1;
+        item.size = Math.round((item.size * scale * 100) / sizeToFill);
+      });
+    }
+
+    // Ensure items add up to 100 in case of rounding error.
+    totalSize = flexItems.reduce((total, item) => total + item.size, 0);
+    const excess = Math.round(100 - totalSize);
+
+    if (excess) {
+      const _index = index !== undefined && !items[index].fixed ? index : items.length - 1;
+      items[_index].size += excess;
     }
   }
 
-  /**
-   * Scales items proportionally so total is equal to 100.
-   * Assumes that an item was removed from array.
-   * @param {*} items
-   */
-  function sizeToFill(items) {
-    if (items.length === 0) {
-      return;
+  function toggleFixed(index, fixed) {
+    let addExcessToContainer;
+    const remainingItems = containers.value.slice();
+    const container = remainingItems.splice(index, 1)[0];
+
+    if (container.fixed !== fixed) {
+      if (fixed) {
+        const sizeToFill = 100 - container.size;
+        container.size = Math.round((container.size / 100) * getElSize());
+        remainingItems.forEach((item) => {
+          const scale = item.scale ?? 1;
+          item.size = Math.round((item.size * scale * 100) / sizeToFill);
+        });
+      } else {
+        container.size = Math.round((container.size * 100) / (getElSize() + container.size));
+        addExcessToContainer = index;
+        const remainingSize = 100 - container.size;
+        remainingItems.forEach((item) => {
+          const scale = item.scale ?? 1;
+          item.size = Math.round((item.size * scale * remainingSize) / 100);
+        });
+      }
+
+      container.fixed = fixed;
+      sizeItems(containers.value, addExcessToContainer);
+      callback?.();
     }
+  }
 
-    const oldTotal = items.reduce((total, item) => total + item.size, 0);
-    items.forEach((item) => {
-      const itemScale = item.scale || 1;
-      item.size = Math.round((item.size * itemScale * 100) / oldTotal);
-    });
+  function sizeFixedContainer(index, size) {
+    const container = containers.value[index];
 
-    // Ensure items add up to 100 in case of rounding error.
-    const total = items.reduce((t, item) => t + item.size, 0);
-    const excess = Math.round(100 - total);
-    items[items.length - 1].size += excess;
+    if (container.fixed) {
+      container.size = size;
+
+      callback?.();
+    } else {
+      console.warn('Use view drag resizing to resize flexible containers.');
+    }
   }
 
   return {
     addContainer,
     removeContainer,
     reorderContainers,
+    setContainers,
     containers,
     startContainerResizing,
     containerResizing,
-    endContainerResizing
+    endContainerResizing,
+    toggleFixed,
+    sizeFixedContainer
   };
 }