Substitutions are variables. They are declared in any document and defined in the conf.py file, rst_prolog setting.
Caution
Do not use substitutions in headings. The reason is the text that replaces the variable may be longer than the line that is over or below the text and this will produce an error.
Projects using the theme can use the following substitutions:
|v| for
|x| for
To add substitutions within Code blocks, pass the option :substitutions: to the code-block directive.
For example:
.. code-block::
:substitutions:
|rst|
Renders as:
restructuredText