She leet no morsel from hir lippes falle,
Ne wette hir fyngres in hir sauce depe;
Wel koude she carie a morsel and wel kepe
That no drope ne fille upon hire brest.
In curteisie was set ful muchel hir lest.
(General Prologue, I.128-32)
Books of manners -- courtesy books -- were a popular genre in the later Middle Ages, as manners and language became increasingly important in defining the "gentle" classes. The Roman de la rose devotes a great deal of attention to the mattes, notably to the table manners proper to a would-be lady, portions of which are echoed in the portrait of the Prioress in the General Prologue:
The genre of the courtesy book may have had its origin in the monasteries, where young boys were trained to take their part in the community. One such, the Latin Vrbanitatis, intended originally for young monastics, was translated into English in the fifteenth century:
A similar work is "The Little Childrenes Little Boke," which is especially interesting because of its association of good manners with religion (as in the Middle English poem Pearl), and its frequent reminders that manners define social class (at least as it is perceived by others):
The two English texts listed above are from The Babees Book, ed. F. J. Furnivall, EETS 32, 1868 [Wid 11472.32.1], a fascinating collection of such materials.
For an interesting study of the importance of courtesy books to an understanding of the literature of the time, see:
Jonathan Nicholls, The Matter of Courtesy: Medieval Courtesy Books and the Gawin-Poet, Woodbridge, Suffolk, 1985 [PR 1972.G353 N5 1985].