Editing TeX (section)

=== Public domain ===
Since the source code of TeX is essentially in the [[public domain]] (see below), other programmers are allowed (and explicitly encouraged) to improve the system, but are required to use another name to distribute the modified TeX, meaning that the [[source code]] can still evolve. For example, the [[Omega (TeX)|Omega]] project was developed after 1991, primarily to enhance TeX's multilingual typesetting abilities.<ref>{{Cite web|url=https://texfaq.org/FAQ-enginedev|title=TeX Engine development|date=2018-05-24|website=The TeX FAQ|access-date=2019-07-21|archive-date=28 April 2019|archive-url=https://web.archive.org/web/20190428184859/https://texfaq.org/FAQ-enginedev|url-status=dead}}</ref> Knuth created "unofficial" modified versions, such as [[TeX-XeT]], which allows a user to mix texts written in [[Bi-directional text|left-to-right and right-to-left]] [[writing system]]s in the same document.<ref name="autogenerated1"/>