# Schema

Unlike many other editors, tiptap is based on a [schema](https://prosemirror.net/docs/guide/#schema) that defines how your content is structured. This allows you to define the kind of nodes that may occur in the document, its attributes and the way they can be nested.

This schema is *very* strict. You can’t use any HTML-element or attribute that is not defined in your schema.

For example if you paste something like `This is <strong>important</strong>` into tiptap and don’t have registered any extension that handles `strong` tags, you’ll only see `This is important`.

## How a schema looks like

The most simple schema for a typical *ProseMirror* editor is looking something like that.

```js
{
  nodes: {
    document: {
      content: 'block+',
    },
    paragraph: {
      content: 'inline*',
      group: 'block',
      parseDOM: [{ tag: 'p' }],
      toDOM: () => ['p', 0],
    },
    text: {
      group: 'inline',
    },
  },
}
```

We register three nodes here. `document`, `paragraph` and `text`. `document` is the root node which allows one or more block nodes as children (`content: 'block+'`). Since `paragraph` is in the group of block nodes (`group: 'block'`) our document can only contain paragraphs. Our paragraphs allow zero or more inline nodes as children (`content: 'inline*'`) so there can only be `text` in it. `parseDOM` defines how a node can be parsed from pasted HTML. `toDOM` defines how it will be rendered in the DOM.

In tiptap we define every node in its own `Extension` class instead. This allows us to split logic per node. Under the hood the schema will be merged together.

```js
class Document extends Node {
  name = 'document'
  topNode = true

  schema() {
    return {
      content: 'block+',
    }
  }
}

class Paragraph extends Node {
  name = 'paragraph'

  schema() {
    return {
      content: 'inline*',
      group: 'block',
      parseDOM: [{ tag: 'p' }],
      toDOM: () => ['p', 0],
    }
  }
}

class Text extends Node {
  name = 'text'

  schema() {
    return {
      group: 'inline',
    }
  }
}
```
