Substitutions and replacement variables

Like most languages, ReST and MyST both have direct ways to substitute variables to locally customize lessons. While this works for simple cases, this can quickly become difficult to manage with the “master copy” of possibly important content being separated from the main body, and keeping the substitutions up to date.

sphinx_ext_substitution tries to solve these problems by keeping the default values within the document and providing tools to manage the substitution as the context changes over time. It is tested with ReST and should work with MyST as well.