Always ok: putting words on the formality or lack thereoff of your wedding,
where? I don't know. I wouldn't put it on the main invite but in the insert about the venue.
how? either bluntly, on it's own: "black tie wedding at Castle Chez Martin" or subtly implied "followed by a casual brunch".
Actually the strictest of traditional etiquette -does- have you put this on the main invitation. In the lower right corner.
Always ok: a notice about the venue or weather. (soft grass, gravel path from parking to ceremony..)
Where: insert with venue info, website or word of mouth.
Special circumstances: themed wedding (medieval, rétro chic..).
A note about if guests have to
wear specific (period) things, if there will be spare that they can borrow, where can they find it, the difference between renaissance and victorian*...
On the website is best.
(* I'd think that was nitpicking if the HC were to pout because someone mixed the two but hey, example ).
Special circumstances: religious venues when not all your guests share the same faith.
I wouldn't know of the top of my head if a Boudist meditation venues allowed women to show hair or bare shoulders for examples. Even inside the same religion some venues/denominations are more strict so a head up about the don't
can be a normal and appreciated thing.
"we would like our guest to take notice that the Green church ask of the women to cover their shoulders while inside the venue, shawls will be available before entering the church".
I remember a webpage detailing all the differences between black tie, formal,... wear for men, with examples of the suits and a description. The same might exist for women so I'd google if I was uncertain. I just need something to google so something should clue me in from the invite.
Do (or implication of DO) would guide me, Don't would feel like you don't trust me to not come to your Black Tie wedding in hiking boots. Do/Don't
are strong words. "please refrain", "you might find that X would be more comfortable due to the ground", "for you confort, favor flat heels"... will go much easier with me.