The origin of the name, according to the Diccionario de Mexicanísimos, is that at one time these delicate tamales were cooked inside small bags of fine chambray. Now they are wrapped in corn husks or banana leaves. This banana-leaf version is adapted from a recipe I learned from Yolanda Cacho in Juchitán.
If desired, cut the raisins in half and soak in a little warm sherry before adding to the filling. However, this is never done in Oaxaca.