In the gentler past, one inferred by the time of day the form of the invitation and the locale what one would wear: Morning, evening with engraved invitations at a church or home: formal, white tie. The bride would wear a formal floor lenght gown with a long veil Afternoon at home or hotel with handwritten invites: semi-formal and tuxes. The bride in waltz or tea lenght dress, fingertip veil Printed invites to beaches, other locales, informal. but that meant dressy dresses and business suits, not sandals and shorts. The bride in street length dress with a short chin lenght veil. Nothing would be so stated on the invites, because that would say the invitees were too...naive? to know the rules. And only a 1st time bride(supposedly saying she was a virgin) would wear white.
But time moves on. My daughter wore a long white dress to her second wedding in her backyard at 11 in the morning, no veil, the groom wore khaki bermuda shorts, Hawaiian print shirt and Birkenstock sandals with no socks. The guests showed up in anything from shorts to jeans. It really was lovely. Not traditional at all. Even the woman minister wore a pant suit.
I guess it's like quilting now: no rules, if it works, its fine.