Hypertext Markup Language

<cite>

For titles of works.

<details>

For sections of stuff you can show/hide. Added a <summary> to set the title. Use <details open> to make it start unfolded.

<dfn>

For specifying first instance of a term. Use with <abbr> or <acronym>.

<figure>

For images associated stuffs. Put a regular 'ol <img> in there and use <figcaption> for a caption.

<kbd>

For keyboard / button instructions.