restructure the content, improve a lot

docs/src/docPages/guide/custom-extensions.md

@@ -25,8 +25,114 @@ new Editor({
 })
 ```
 
-You can overwrite every aspect of an existing extension. [Read more about that here.](/guide/custom-extensions/overwrite-defaults)
+You can overwrite every aspect of an existing extension:
+
+### Name
+
+```js
+import Document from '@tiptap/extension-document'
+
+const CustomDocument = Document()
+  .name('doc')
+  .create()
+```
+
+### Settings
+
+```js
+import Heading from '@tiptap/extension-heading'
+
+const CustomHeading = Heading()
+  .defaults({
+    levels: [1, 2, 3],
+    class: 'my-custom-heading',
+  })
+  .create()
+```
+
+### Schema
+
+```js
+import Code from '@tiptap/extension-code'
+
+const CustomCode = Code()
+  .schema(() => ({
+    excludes: '_',
+    parseDOM: [
+      { tag: 'code' },
+    ],
+    toDOM: () => ['code', { 'data-attribute': 'foobar' }, 0],
+  }))
+  .create()
+```
+
+### Commands
+
+```js
+import Paragraph from '@tiptap/extension-paragraph'
+
+const CustomParagraph = Paragraph()
+  .commands(() => ({
+    paragraph: () => ({ commands }) => {
+      return commands.toggleBlockType(name, 'paragraph')
+    },
+  }))
+  .create()
+```
+
+### Keyboard shortcuts
+
+```js
+import BulletList from '@tiptap/extension-bullet-list'
+
+const CustomBulletList = BulletList()
+  .keys(({ editor }) => ({
+    'Mod-l': () => editor.bulletList(),
+  }))
+  .create()
+```
+
+### Input rules
+
+```js
+import Strike from '@tiptap/extension-strike'
+import { markInputRule } from '@tiptap/core'
+
+const inputRegex = /(?:^|\s)((?:~)((?:[^~]+))(?:~))$/gm
+
+const CustomStrike = Strike()
+  .inputRules(({ type }) => [
+    markInputRule(inputRegex, type),
+  ])
+  .create()
+```
+
+### Paste rules
+
+```js
+import Underline from '@tiptap/extension-underline'
+import { markPasteRule } from '@tiptap/core'
+
+const pasteRegex = /(?:^|\s)((?:~)((?:[^~]+))(?:~))$/gm
+
+const CustomUnderline = Underline()
+  .pasteRules(({ type }) => [
+    markPasteRule(pasteRegex, type),
+  ])
+  .create()
+```
 
 ## Option 2: Extend existing extensions
 
 ## Option 3: Start from scratch
+
+### 1. Read the documentation
+Although tiptap tries to hide most of the complexity of ProseMirror, it’s built on top of its APIs and we recommend you to read through the [ProseMirror Guide](https://ProseMirror.net/docs/guide/) for advanced usage. You’ll have a better understanding of how everything works under the hood and get more familiar with many terms and jargon used by tiptap.
+
+### 2. Have a look at existing extensions
+
+### 3. Get started
+
+### 4. Ask questions
+
+### 5. Publish a community extension