Nested footnotes do not render

Bug
1

When creating t/63172/79, I noticed that:

[^2]

[^2]: [^4]

    [^4]: placeholder

…produces:

#
#639×539 56.4 KB

…whereas:

[^2]

[^2]: [^4]

[^4]: placeholder

…produces:

#
#639×539 57.1 KB

GitHub and GitLab-Flavoured Markdown support this. Being able to nest visible content in side a footnote is important. This solely appears to affect the appear-upon-hover mode.