# Advanced topics

- [Modes](/xforms/xbl-components/advanced-topics/modes.md)
- [JavaScript companion classes](/xforms/xbl-components/advanced-topics/javascript-companion-classes.md)
- [XBL library](/xforms/xbl-components/advanced-topics/xbl-library.md)
- [Extensions](/xforms/xbl-components/advanced-topics/extensions.md)