external directive is not working

[rgaiacs]

The external directive in

mybinder.org-user-guide/docs/about/team.md

Line 8 in af5461c

The Binder Team is a subset of the {external:tc:ref}`JupyterHub Core Team <jupyterhub-team>`.

is not working.

Observed

https://mybinder.readthedocs.io/en/latest/about/team.html has

The Binder Team is a subset of the .

Expected

The external directive to include a link.

More details

The problematic line was added by @choldgraf. @choldgraf could you provide more details about this external directive? Thanks!