Looked it up for everyone searching for it.
Date: July 2017
Source: https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/text/Html.java
Html.fromHtml supports:
- p
- ul
- li
- div
- span
- strong
- b
- em
- cite
- dfn
- i
- big
- small
- font
- blockquote
- tt
- a
- u
- del
- s
- strike
- sup
- sub
- h1
- h2
- h3
- h4
- h5
- h6
- img
- br