myst-parser (github) supports sphinx roles.

Quick links:

• sphinx.ext.doctest (source: sphinx/ext/doctest.py)
• Related: How does xdoctest work with the Sphinx doctest extension?  Erotemic/xdoctest#68
• Also referenced
• as of today at v0.18.0 these are parsed as nodes.literal_block not nodes.doctest_block (message)
• Potentially useful: https://gist.github.com/tonyfast/cfb55f41f5452ef33ec6fbb4e0bda991

Normal directive syntax:

```{doctest}

>>> print(1 + 2)
3
```

eval-rst directive:

```{eval-rst}

.. doctest::

   >>> print(1 + 2)
   3
```