Specification structure of a set of LaTeX commands.
The specification will be passed to MiTeX for converting LaTeX code correctly. For example, MiTeX Parser uses it to produce an AST that respect the shape of commands.
Note: since we need to process environments statically, users cannot
override the \begin and \end commands.
See https://github.com/mitex-rs/mitex/blob/main/docs/spec.typ for detailed description.