Can someone please explain to me how the User Card pop-up works?

Development
2

I think you’re looking for card-contents-base.js.es6, which defines a series of events which point to the _show method.

# card-contents-base.js.es6#103
$("#main-outlet").on(clickDataExpand, `[data-${id}]`, e => {});

$("#main-outlet").on(clickMention, `a.${triggeringLinkClass}`, e => {});

this.appEvents.on(previewClickEvent, $target => {});

# card-contents-base.js.es6#20
_show(username, $target) {}