Add option to show only chat messages (hide joins, quits etc.)

[clue]

This can be implemented in pure CSS which makes this super fast. The question is if and where we want to save this setting. The interface is currently entirely stateless.

input[type=checkbox] {
    /* … */
}
input:checked ~ article {
    display: none;
}
input:checked ~ article.chat {
    display: block;
}