Optional content [PDF:1.6:4.10], also known as layered content.

It refers to sections of content in a PDF document that can be selectively viewed or hidden by document authors or consumers. This capability is useful in items such as CAD drawings, layered artwork, maps, and multi-language documents.

## Related Documentation

For overviews, tutorials, examples, guides, and tool documentation, please see:

- PDF Clown Home Page