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.
” 由于TeX的源代码基本上处于公共领域，其他程序员可以（并明确被鼓励）改进系统，但需要使用其他名称来分发修改后的TeX。