diff --git a/packages/core/build.js b/packages/core/build.js
index 7248b245c69..b18711312e6 100644
--- a/packages/core/build.js
+++ b/packages/core/build.js
@@ -48,8 +48,8 @@ let result
     ...options,
     minify: false,
     sourcemap: false,
-    outfile: 'tests/dist/index.mjs',
-    format: 'esm',
+    outfile: 'tests/dist/index.js',
+    format: 'cjs',
     external: [],
   })
   .catch(() => process.exit(1))
diff --git a/packages/core/src/utils.js b/packages/core/src/utils.js
index 35fcff2397d..5283ac147c8 100644
--- a/packages/core/src/utils.js
+++ b/packages/core/src/utils.js
@@ -397,6 +397,75 @@ const addPartOptions = (part, config) => {
     }
   }
   if (part.from) addPartOptions(part.from, config)
+  if (part.after) {
+    if (Array.isArray(part.after)) {
+      for (const dep of part.after) addPartOptions(dep, config)
+    } else addPartOptions(part.after, config)
+  }
+
+  return config
+}
+
+// Helper method for detecting a array with only strings
+const isStringArray = val => (Array.isArray(val) && val.length > 0)
+  ? val.reduce((prev=true, cur) => (prev && typeof cur === 'string'))
+  : false
+// Helper method for detecting an object
+const isObject = obj => obj && typeof obj === 'object'
+
+// Hat-tip to jhildenbiddle => https://stackoverflow.com/a/48218209
+const mergeOptionSubgroup = (...objects) => objects.reduce((prev, obj) => {
+  Object.keys(obj).forEach(key => {
+    const pVal = prev[key];
+    const oVal = obj[key];
+
+    if (Array.isArray(pVal) && Array.isArray(oVal)) {
+      prev[key] = pVal.concat(...oVal);
+    }
+    else if (isObject(pVal) && isObject(oVal)) {
+      prev[key] = mergeOptionSubgroup(pVal, oVal);
+    }
+    else {
+      prev[key] = oVal;
+    }
+  })
+
+  return prev
+}, {})
+
+const mergeOptionGroups = (cur, add) => {
+  if (isStringArray(cur) && isStringArray(add)) return [...new Set([...cur, ...add])]
+  else if (!Array.isArray(cur) && !Array.isArray(add)) return mergeOptionSubgroup(cur, add)
+  else {
+    const all = [...cur]
+    for (const entry of add) {
+      if (typeof add === 'string' && all.indexOf(entry) === -1) all.push(entry)
+      else all.push(entry)
+    }
+    return all
+  }
+
+  return cur
+}
+
+// Add part-level optionGroups
+const addPartOptionGroups = (part, config) => {
+  if (typeof config.optionGroups === 'undefined') {
+    if (part.optionGroups) config.optionGroups = part.optionGroups
+    return config
+  }
+  if (part.optionGroups) {
+    for (const group in part.optionGroups) {
+      if (typeof config.optionGroups[group] === 'undefined') config.optionGroups[group] = part.optionGroups[group]
+      else config.optionGroups[group] = mergeOptionGroups(config.optionGroups[group], part.optionGroups[group])
+    }
+  }
+  if (part.from) addPartOptionGroups(part.from, config)
+  if (part.after) {
+    if (Array.isArray(part.after)) {
+      for (const dep of part.after) addPartOptionGroups(dep, config)
+    } else addPartOptionGroups(part.after, config)
+  }
 
   return config
 }
@@ -410,6 +479,11 @@ const addPartMeasurements = (part, config, list=false) => {
     for (const m of part.measurements) list.push(m)
   }
   if (part.from) addPartMeasurements(part.from, config, list)
+  if (part.after) {
+    if (Array.isArray(part.after)) {
+      for (const dep of part.after) addPartMeasurements(dep, config, list)
+    } else addPartMeasurements(part.after, config, list)
+  }
 
   // Weed out duplicates
   config.measurements = [...new Set(list)]
@@ -429,6 +503,11 @@ const addPartOptionalMeasurements = (part, config, list=false) => {
     }
   }
   if (part.from) addPartOptionalMeasurements(part.from, config, list)
+  if (part.after) {
+    if (Array.isArray(part.after)) {
+      for (const dep of part.after) addPartOptionalMeasurements(dep, config, list)
+    } else addPartOptionalMeasurements(part.after, config, list)
+  }
 
   // Weed out duplicates
   config.optionalMeasurements = [...new Set(list)]
@@ -471,6 +550,7 @@ export const addPartConfig = (part, config) => {
   config = addPartMeasurements(part, config)
   config = addPartOptionalMeasurements(part, config)
   config = addPartDependencies(part, config)
+  config = addPartOptionGroups(part, config)
 
   return config
 }
diff --git a/packages/core/tests/pattern.test.js b/packages/core/tests/pattern.test.js
index 57c8f4e383b..a3068ee8bb3 100644
--- a/packages/core/tests/pattern.test.js
+++ b/packages/core/tests/pattern.test.js
@@ -1,5 +1,5 @@
 let expect = require("chai").expect;
-let freesewing = require("../dist/index.js");
+let freesewing = require("./dist/index.js");
 it("Pattern constructor should initialize object", () => {
   let pattern = new freesewing.Pattern({
     foo: "bar",
@@ -1023,3 +1023,97 @@ it("Design constructor should resolve nested dependencies (2022)", () => {
   expect(pattern.parts.partD.paths.d.ops[1].to.x).to.equal(44)
   expect(pattern.parts.partD.paths.d.ops[1].to.y).to.equal(44)
 })
+it("Pattern should merge optiongroups", () => {
+  const partA = {
+    name: "partA",
+    options: { optionA: { bool: true } },
+    measurements: [ 'measieA' ],
+    optionalMeasurements: [ 'optmeasieA' ],
+    optionGroups: {
+      simple: ['simplea1', 'simplea2', 'simplea3'],
+      nested: {
+        nested1: [ 'nested1a1', 'nested1a2', 'nested1a3' ],
+      },
+      subnested: {
+        subnested1: [
+          'subnested1a1',
+          'subnested1a2',
+          'subnested1a3',
+          {
+            subsubgroup: [
+              'subsuba1',
+              'subsuba2',
+              {
+                subsubsubgroup: [ 'subsubsub1', 'simplea1' ],
+              }
+            ]
+          }
+        ]
+      }
+    },
+    draft: part => part,
+  }
+  const partB = {
+    name: "partB",
+    from: partA,
+    options: { optionB: { pct: 12, min: 2, max: 20 } },
+    measurements: [ 'measieB' ],
+    optionalMeasurements: [ 'optmeasieB', 'measieA' ],
+    optionGroups: {
+      simple: ['simpleb1', 'simpleb2', 'simpleb3'],
+      bsimple: ['bsimpleb1', 'bsimpleb2', 'bsimpleb3'],
+      nested: {
+        nested2: [ 'nested2b1', 'nested2b2', 'nested2b3' ],
+      },
+      subnested: {
+        subnested1: [
+          'subnested1b1',
+          'subnested1b2',
+          'subnested1b3',
+          {
+            subsubgroup: [
+              'subsubb1',
+              'subsubb2',
+              {
+                subsubsubgroup: [ 'bsubsubsub1', 'simplea1' ],
+              }
+            ]
+          }
+        ]
+      }
+    },
+    draft: part => part,
+  }
+  let Design, pattern
+  try {
+    Design = new freesewing.Design({ parts: [ partB ] });
+    pattern = new Design().init()
+  } catch(err) {
+    console.log(err)
+  }
+  const og = pattern.config.optionGroups
+  expect(og.simple.length).to.equal(6)
+  expect(og.simple.indexOf('simplea1') === -1).to.equal(false)
+  expect(og.simple.indexOf('simplea2') === -1).to.equal(false)
+  expect(og.simple.indexOf('simplea3') === -1).to.equal(false)
+  expect(og.simple.indexOf('simpleb1') === -1).to.equal(false)
+  expect(og.simple.indexOf('simpleb2') === -1).to.equal(false)
+  expect(og.simple.indexOf('simpleb3') === -1).to.equal(false)
+  expect(og.nested.nested1.length).to.equal(3)
+  expect(og.nested.nested1.indexOf('nested1a1') === -1).to.equal(false)
+  expect(og.nested.nested1.indexOf('nested1a2') === -1).to.equal(false)
+  expect(og.nested.nested1.indexOf('nested1a3') === -1).to.equal(false)
+  expect(og.nested.nested2.length).to.equal(3)
+  expect(og.nested.nested2.indexOf('nested2b1') === -1).to.equal(false)
+  expect(og.nested.nested2.indexOf('nested2b2') === -1).to.equal(false)
+  expect(og.nested.nested2.indexOf('nested2b3') === -1).to.equal(false)
+  expect(og.subnested.subnested1.length).to.equal(8)
+  expect(og.subnested.subnested1.indexOf('subnested1a1') === -1).to.equal(false)
+  expect(og.subnested.subnested1.indexOf('subnested1a2') === -1).to.equal(false)
+  expect(og.subnested.subnested1.indexOf('subnested1a3') === -1).to.equal(false)
+  expect(og.subnested.subnested1.indexOf('subnested1b1') === -1).to.equal(false)
+  expect(og.subnested.subnested1.indexOf('subnested1b2') === -1).to.equal(false)
+  expect(og.subnested.subnested1.indexOf('subnested1b3') === -1).to.equal(false)
+  // FIXME: Some work to be done still with deep-nesting of groups with the same name
+})
+