Do you sit shiva on Purim?
The Rambam writes that although Purim is a day forbidden in fasting and hespedim, one continues to sit shiva as usual (Avelus 11:5).
However, the Rosh (Moed Katan 85) writes that one does not sit shiva.
The Shulchan Aruch (696) rules in accordance with the Rambam, whereas the Rema cites the ruling of the Rosh, adding that this is the custom.
Yet, elsewhere the Shulchan Aruch (Yoreh De’ah 401:7) writes that one does not sit shiva on Purim. This is the common custom.