Siman 524

One may not climb a tree on Yom Tov, a decree lest one pluck. And one may not ride upon an animal, a decree lest one cut a branch. And in the Yerushalmi it says because of the resting of his animal, and in siman 246 we explained this, see there and in siman 495 whether there is the resting of his animal or not. And one may not swim upon the surface of the water, a decree lest one make a swimming barrel. And it is a vessel of reeds that they make in the form of a barrel, and they learn to swim with it.

And we do not clap with the palm on the thigh, nor do we clap palm to palm, whether one does this due to anger or whether one does this due to joy, as a decree lest he repair a musical instrument. And the Rambam explained that this refers to the melody produced by striking a cymbal. And likewise, we do not dance for this reason, but it is customary to be lenient regarding dancing (Levush). And it seems to me that even regarding palm to palm they are not careful, and perhaps the reason is because we are not experts in the repairing of musical instruments.

And we do not judge, and we do not proscribe like the proscriptions of priests, and we do not consecrate, and we do not make valuations, and we do not set aside terumot and ma'asrot. And so too, we do not betroth a woman, and we do not enter the huppah, and we do not perform yibbum, and we do not perform halizah. And it is forbidden to betroth even when he does not have a wife and children. And the opinion of our teacher Tam is that in such a case it is permitted, but this is not the opinion of Rashi and the Rambam and the Rosh. And we do not divorce, even with a get that was written on the eve of the Yom Tov and by means of a messenger. However, in the case of a person on his deathbed, where we see that the world is overpowering him, and she might remain bound to a yavam – he may give it to her even on Shabbat, and all the more so on Yom Tov. (And that which is implied in Ketubot 47a that there is entry into the huppah on Shabbat – this is from the Torah. And see Magen Avraham and Eliyah Rabbah).

The Tur wrote that regarding all of these, if they performed them, whether inadvertently or intentionally—what he has done is done. Thus far his words. And we do not say in this case "if one performed it, it is not effective," as I wrote in Choshen Mishpat siman 208 regarding the matter of a sale on Shabbat. And see what I wrote in Yoreh Deah siman 230 (and see Taz).