See the demo site

Displays text on a ribbon or corner

syntax 1 (body) : {up corner=text}
syntax 2 (block) : {up corner=text}content of the block{/up corner}

🟩 upbtn-makefile PREFS.INI :
new : corner=Nouveau | position=bottom-left | bgcolor=violet | color=yellow

▼

position, size and style of the corner

if the corner is clickable

style of the block if the shortcode has content

style and secondary options