What is ε-TeX?

The $epsilon$-TeX extensions to TeX are a range of new functionalities added by the NTS to Knuth’s original TeX program: see [details of engine developments](FAQ-enginedev) for more.

In a modern TeX distribution, the extensions are enabled for almost all formats except Knuth’s TeX (tex) itself. As such, most users will never use a system not featuring $epsilon$-TeX: indeed, LaTeX2e has required them since 2017.