# useUndoBoundary

Source: https://sdk.pdf.net/docs/v1/reference/useUndoBoundary



Returns a function that keeps the next edit out of the previous undo step, such as for making an AI-driven or automated change undoable separately from the user's typing around it.

```ts
const markUndoBoundary = useUndoBoundary()

markUndoBoundary()
```

Edits made within 500 ms of each other merge into a single undo step, even when they come from different hook calls (see [useUndoRedo](https://sdk.pdf.net/docs/v1/reference/useUndoRedo)). A boundary ends the current step, so the next edit starts a new one.

## Behavior [#behavior]

* Call it before an operation, and again after all its edits finish, so the operation doesn't merge with the edits before or after it.
* A boundary doesn't guarantee that the operation becomes a single undo step: pauses between its edits, or changes on different pages, can split it into several.
* The call itself doesn't create an empty undo step, doesn't change the [document revision](https://sdk.pdf.net/docs/v1/reference/useDocumentRevision), and keeps the redo history.
* Throws `DocumentNotLoadedError` when no document is loaded.

## Example [#example]

```tsx
import { useProgrammaticEditor, useUndoBoundary } from '@sdk-pdf/react'

function useReplaceParagraphText() {
  const markUndoBoundary = useUndoBoundary()
  const { getParagraphEditor } = useProgrammaticEditor()

  return (paragraphId: string, text: string) => {
    const editor = getParagraphEditor(paragraphId)
    if (!editor) return

    markUndoBoundary()
    try {
      editor.selectAll()
      editor.insertText(text)
    } finally {
      markUndoBoundary()
    }
  }
}
```