Although isru chag, the day following Pesach, Shavuot and Sukkot, is widely
observed as a moderately joyous day, the halakhic literature is hardly in
unanimous support. Rif, Rambam and Rosh fail to codify isru chag. What is more,
as noted by Magen Avraham (O.C. 429:8, 494:3; see