As of T4119:

• some blockquotes can have headers; and
• blockquotes can nest.

These could probably use some refinement, particularly in the header case.

Write a header with >>!. Quote with >. Multiple > nests the quote. Here are some examples:

replying author wrote:

original author wrote:

i have an opinion

your opinion is bad, and you are bad

beep

boop

bip

blip