diff --git a/packages/core/src/defs.mjs b/packages/core/src/defs.mjs
new file mode 100644
index 00000000000..1e1955a2d65
--- /dev/null
+++ b/packages/core/src/defs.mjs
@@ -0,0 +1,94 @@
+//////////////////////////////////////////////
+//               CONSTRUCTOR                //
+//////////////////////////////////////////////
+
+/**
+ * Constructor for Defs
+ *
+ * @constructor
+ * @return {Defs} this - The Defs instance
+ */
+export function Defs() {
+  this.list = {}
+
+  return this
+}
+
+//////////////////////////////////////////////
+//            PUBLIC METHODS                //
+//////////////////////////////////////////////
+
+/**
+ * Return a deep copy of this
+ *
+ * @return {object} this - The Defs instance
+ */
+Defs.prototype.clone = function () {
+  let clone = new Defs()
+  clone.list = JSON.parse(JSON.stringify(this.list))
+
+  return clone
+}
+
+/**
+ * Retrieve a def
+ *
+ * @param {string} name - Name of the def to get
+ * @return value - The value under name
+ */
+Defs.prototype.get = function (name) {
+  if (typeof this.list[name] === 'undefined') return false
+  else return this.list[name]
+}
+
+/**
+ * Remove a def
+ *
+ * @param {string} name - Name of the def to set
+ * @return {object} this - The Defs instance
+ */
+Defs.prototype.remove = function (name) {
+  delete this.list[name]
+
+  return this
+}
+
+/**
+ * Return SVG code for Defs
+ *
+ * @return {string} svg - The SVG code
+ */
+Defs.prototype.render = function () {
+  let svg = ''
+  for (let key in this.list) {
+    svg += ` ${key}="${this.list[key].join('')}"`
+  }
+
+  return svg
+}
+
+/**
+ * Set a def, overwriting existing value
+ *
+ * @param {string} name - Name of the defs to set
+ * @param {string} value - Value of the defs to set
+ * @return {Defs} this - The Defs instance
+ */
+Defs.prototype.set = function (name, value) {
+  this.list[name] = [value]
+
+  return this
+}
+
+/**
+ * Sets a def, but only if it's not currently set
+ *
+ * @param {string} name - Name of the def to set
+ * @param {string} value - Value of the def to set
+ * @return {Defs} this - The Defs instance
+ */
+Defs.prototype.setIfUnset = function (name, value) {
+  if (typeof this.list[name] === 'undefined') this.list[name] = [value]
+
+  return this
+}
diff --git a/packages/core/src/svg.mjs b/packages/core/src/svg.mjs
index d77412ce6ac..0dd58f963ea 100644
--- a/packages/core/src/svg.mjs
+++ b/packages/core/src/svg.mjs
@@ -1,4 +1,5 @@
 import { Attributes } from './attributes.mjs'
+import { Defs } from './defs.mjs'
 import { __addNonEnumProp, round } from './utils.mjs'
 import { version } from '../data.mjs'
 
@@ -31,7 +32,7 @@ export function Svg(pattern) {
   this.layout = {}
   this.body = ''
   this.style = ''
-  this.defs = ''
+  this.defs = new Defs()
 }
 
 //////////////////////////////////////////////
@@ -215,7 +216,7 @@ Svg.prototype.__renderCircle = function (point) {
 Svg.prototype.__renderDefs = function () {
   let svg = '<defs>'
   this.__indent()
-  svg += this.__nl() + this.defs
+  svg += this.__nl() + this.defs.render()
   this.__outdent()
   svg += this.__nl() + '</defs>' + this.__nl()
 
diff --git a/plugins/plugin-annotations/src/buttons.mjs b/plugins/plugin-annotations/src/buttons.mjs
index e49f78c36c4..6c54b94d8ca 100644
--- a/plugins/plugin-annotations/src/buttons.mjs
+++ b/plugins/plugin-annotations/src/buttons.mjs
@@ -1,6 +1,7 @@
 const defs = [
-  // button
-  `
+  {
+    name: 'button',
+    def: `
 <g id="button">
   <circle
     cx="0" cy="0" r="3.4"
@@ -11,8 +12,10 @@ const defs = [
   <circle cx="1"  cy="1"  r="0.5" class="no-stroke fill-mark" />
   <circle cx="-1" cy="1"  r="0.5" class="no-stroke fill-mark" />
 </g>`,
-  // buttonhole
-  `
+  },
+  {
+    name: 'buttonhole',
+    def: `
 <g id="buttonhole">
   <path
     class="mark"
@@ -31,8 +34,10 @@ const defs = [
     d="M -1,0 L 1,0 L 1,10 L -1,10 z"
   />
 </g>`,
-  // snaps
-  `
+  },
+  {
+    name: 'snaps',
+    def: `
 <radialGradient id="snap-stud-grad" cx="50%" cy="50%" r="50%" fx="50%" fy="50%">
   <stop offset="30%" style="stop-color:rgb(235,235,235); stop-opacity:1"/>
   <stop offset="80%" style="stop-color:rgb(100,100,100);stop-opacity:1" />
@@ -61,6 +66,7 @@ const defs = [
     d="M -1.7,-1 L -1.7,1 M 1.7,-1 L 1.7,1" id="snap-socket-lines"
   />
 </g>`,
+  },
 ]
 
 // Export hooks
@@ -68,7 +74,7 @@ export const buttonsHooks = {
   preRender: [
     function (svg) {
       for (const def of defs) {
-        if (svg.defs.indexOf(def) === -1) svg.defs += def
+        svg.defs.setIfUnset(def.name, def.def)
       }
     },
   ],
diff --git a/plugins/plugin-annotations/src/cutonfold.mjs b/plugins/plugin-annotations/src/cutonfold.mjs
index e98ae2dd818..1a5d76073b4 100644
--- a/plugins/plugin-annotations/src/cutonfold.mjs
+++ b/plugins/plugin-annotations/src/cutonfold.mjs
@@ -11,7 +11,7 @@ const markers = `
 export const cutonfoldHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf(markers) === -1) svg.defs += markers
+      svg.defs.setIfUnset('cutonfold', markers)
     },
   ],
 }
diff --git a/plugins/plugin-annotations/src/dimensions.mjs b/plugins/plugin-annotations/src/dimensions.mjs
index 52e777fc371..3e975eb0aca 100644
--- a/plugins/plugin-annotations/src/dimensions.mjs
+++ b/plugins/plugin-annotations/src/dimensions.mjs
@@ -74,7 +74,7 @@ function lleader(so, type, props, id) {
 export const dimensionsHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf(markers) === -1) svg.defs += markers
+      svg.defs.setIfUnset('dimensions', markers)
     },
   ],
 }
diff --git a/plugins/plugin-annotations/src/grainline.mjs b/plugins/plugin-annotations/src/grainline.mjs
index a2203925ae9..d04267b3bde 100644
--- a/plugins/plugin-annotations/src/grainline.mjs
+++ b/plugins/plugin-annotations/src/grainline.mjs
@@ -12,7 +12,7 @@ const dflts = { text: 'grainline' }
 export const grainlineHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf(markers) === -1) svg.defs += markers
+      svg.defs.setIfUnset('grainline', markers)
     },
   ],
 }
diff --git a/plugins/plugin-annotations/src/logo.mjs b/plugins/plugin-annotations/src/logo.mjs
index 92639ea4fe2..3b23908fa4b 100644
--- a/plugins/plugin-annotations/src/logo.mjs
+++ b/plugins/plugin-annotations/src/logo.mjs
@@ -5,7 +5,7 @@ const logo = (scale) =>
 export const logoHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf('id="logo"') === -1) svg.defs += logo(svg.pattern.settings[0].scale)
+      svg.defs.setIfUnset('logo', logo(svg.pattern.settings[0].scale))
     },
   ],
 }
diff --git a/plugins/plugin-annotations/src/notches.mjs b/plugins/plugin-annotations/src/notches.mjs
index 77764b38aa8..e7e33561de4 100644
--- a/plugins/plugin-annotations/src/notches.mjs
+++ b/plugins/plugin-annotations/src/notches.mjs
@@ -12,7 +12,7 @@ const markers = `
 export const notchesHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf(`id="notch"`) === -1) svg.defs += markers
+      svg.defs.setIfUnset('notch', markers)
     },
   ],
 }
diff --git a/plugins/plugin-annotations/src/pleat.mjs b/plugins/plugin-annotations/src/pleat.mjs
index 0e37b1d85c0..cc0ce01eb44 100644
--- a/plugins/plugin-annotations/src/pleat.mjs
+++ b/plugins/plugin-annotations/src/pleat.mjs
@@ -8,7 +8,7 @@ const markers = `
 export const pleatHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf(markers) === -1) svg.defs += markers
+      svg.defs.setIfUnset('pleat', markers)
     },
   ],
 }
diff --git a/plugins/plugin-annotations/src/sewtogether.mjs b/plugins/plugin-annotations/src/sewtogether.mjs
index 16d2a4aa3f7..54ecb06ee7f 100644
--- a/plugins/plugin-annotations/src/sewtogether.mjs
+++ b/plugins/plugin-annotations/src/sewtogether.mjs
@@ -14,7 +14,7 @@ const markers = `
 export const sewtogetherHooks = {
   preRender: [
     function (svg) {
-      if (svg.defs.indexOf(markers) === -1) svg.defs += markers
+      svg.defs.setIfUnset('sewTogether', markers)
     },
   ],
 }