Just a quick note about some useful HTML tags that have been around for a long time, but I’ve found particularly useful recently:

<del cite="url" datetime="YYYY-MM-DDThh:mm:ssTZD>

Mark text that has been deleted, optionally citing a URL for more details and a date and time of change. Useful for marking alterations to posts.

<del>Example deleted text</del>

< ins cite="url" datetime="date of change >

Mark text that has been inserted, optionally citing a URL for more details and a date and time of change. Useful for marking alterations to posts.

Example inserted text

_Term_

_Definition_

Definition list - example is this list of tags