diff --git a/packages/core/src/utils/getAttributesFromExtensions.ts b/packages/core/src/utils/getAttributesFromExtensions.ts
index 826acc13..62a327c3 100644
--- a/packages/core/src/utils/getAttributesFromExtensions.ts
+++ b/packages/core/src/utils/getAttributesFromExtensions.ts
@@ -7,6 +7,10 @@ import {
   ExtensionAttribute,
 } from '../types'
 
+/**
+ * Get a list of all extension attributes defined in `addAttribute` and `addGlobalAttribute`.
+ * @param extensions List of extensions
+ */
 export default function getAttributesFromExtensions(extensions: Extensions) {
   const extensionAttributes: ExtensionAttribute[] = []
   const { nodeExtensions, markExtensions } = splitExtensions(extensions)
diff --git a/packages/core/src/utils/injectExtensionAttributesToParseRule.ts b/packages/core/src/utils/injectExtensionAttributesToParseRule.ts
index de74cedf..14c7595d 100644
--- a/packages/core/src/utils/injectExtensionAttributesToParseRule.ts
+++ b/packages/core/src/utils/injectExtensionAttributesToParseRule.ts
@@ -1,6 +1,12 @@
 import { ParseRule } from 'prosemirror-model'
 import { ExtensionAttribute } from '../types'
 
+/**
+ * This function merges extension attributes into parserule attributes (`attrs` or `getAttrs`).
+ * Cancels when `getAttrs` returned `false`.
+ * @param parseRule ProseMirror ParseRule
+ * @param extensionAttributes List of attributes to inject
+ */
 export default function injectExtensionAttributesToParseRule(parseRule: ParseRule, extensionAttributes: ExtensionAttribute[]): ParseRule {
   if (parseRule.style) {
     return parseRule