On asciinema-player
version 2.6.1, I tried
<asciinema-player rows="32" poster="data:text/plain,This will be printed as poster\n\rThis in second line" src="/asciicasts/temp.cast"></asciinema-player>
(see poster
attribute) but I get
All the other poster
attribute examples work so I was wondering if I did something wrong. Thank you!