It’s the style for the notice shown on all events in the category, indicating its severity - info/warning/danger (white/yellow/red, and icons corresponding to those severities)…
This doesn’t need comments but rather named placeholders, because they way they are right now it would break if some language were to put the end date first. I don’t know if there’s any language doing this (hopefully not) but in principle a translatable string should only use the generic {} placeholder if there is no more than one in the string. Otherwise {named} placeholders are preferred.