Rare ms. 382 in the collection of the Library at the Katz Center for Advanced Judaic Studies is a mahzor (festive prayerbook) for the autumn holidays according to the Western Ashkenazic rite. It was copied during the fourteenth century, probably in the Rhineland area of southern Germany and northern Italy. It contains the liturgical poetry (piyyutim) recited in the synagogue on both days of Rosh ha-shanah, on Yom Kippur, on the first and second day of Sukkot, the intermediate Sabbath during Sukkot and on Shemini Atseret, but it lacks most of the standard prayers said on these occasions because the precentor would have known these by heart. Today, the volume is incomplete, beginning with musaf (the additional prayers) recited on the first day of Rosh ha-shanah and ending with musaf on Shemini Atseret. In its complete form it would have contained more than 280 folio leaves (rather than the extant 252 folios). In addition to at least two quires missing at the beginning and one quire missing at the end, several pages have been cut out of the manuscript. The manuscript was rebound in (early) modern times and apparently after that was damaged, probably by fire.

During the thirteenth and fourteenth centuries, several changes took place in the production of liturgical manuscripts in Ashkenaz that influenced both the selection of texts and the appearance of the texts on the page. Notwithstanding unifying tendencies, many communities retained their local traditions about which piyyutim to say when, as mirrored by the unusual ordering of yotsrot for Sukkot in the Katz Center's mahzor. Most textual changes that spread throughout many communities pertain to the omission of piyyutim, e.g. many communities decided to abbreviate the recitation of qedushta'ot, the complex compositions adorning the Amidah on Sabbaths and holidays, by skipping parts of the rehitim, the series of highly structured poems in the penultimate position of the qedushta, especially on the high holidays when many piyyutim were recited. The mahzor of the Katz Center displays a selection that is largely in accordance with later habits, although in one case a piyyut that had been omitted by the original scribe was added on the margins by an almost contemporary hand (f. 143r). This note was preserved when the margins were cut at a later time, suggesting that the community using the mahzor continued to recite this piyyut. Interestingly, the mahzor does not share another textual change of the late thirteenth, early fourteenth century, namely the omission of the strings of verses inserted into the first three piyyutim of qedushta'ot, although it rarely contains more than three or four verses, even though earlier manuscripts may have up to seven or eight verses in each string.

Among the piyyutim retained by the original scribe were two anti-Christian piyyutim in the rehitim for shaharit on Yom Kippur that would have appealed to the Jewish communities in Ashkenaz in the thirteenth and fourteenth centuries who could use the liturgy to express their antagonism to Christianity in times of growing tension, but apparently these piyyutim were considered to be superfluous or even dangerous at a later time, when the leafs containing this piyyutim were cut from the mahzor (f. 105 and 108). Only one occasion of the Aleynu is censored (by erasure) while another occasion of the same text was not changed. It is not possible to reconstruct when this drastic measure was taken, nor whether it is a case of self-censure or due only to outside pressure. Cutting out the piyyutim was eased by the selective recitation of rehitim that began in the thirteenth and fourteenth centuries and had led to the omission of some rehitim from the manuscript.

The aesthetic changes in the visual appearance of liturgical manuscripts in Ashkenaz developed during the thirteenth and early fourteenth centuries. Changes in parchment manufacturing brought about a more generous layout with lavish margins, ample space between the lines, sumptuous initial words and—by the end of the thirteenth century—intricate visualizations of poetic structures like acrostics, stanzas, hemistichs and recurring elements. The Katz Center's mahzor displays most of these, although the margins were cut by approximately 1.8 inches on one side, probably by a little less on the other sides, when the volume was rebound in (early) modern times, changing the appearance of the page dramatically, even though the layout is still generous. Some liturgical manuscripts from the fourteenth century use color to mark structure in poetic texts, e.g. for acrostics or biblical verses at the end of stanzas. The mahzor of the Katz Center uses black ink only, with the exception of some dots around the letters of initial words in the Hosha'anot section and the same red ink in the decoration of the beginning of this section. The scribe took however great care to create well-structured and diversified pages with marked acrostics and poetic structures, using larger letters and short lines, sometimes creating the impression of columns of text. He enlarged the initial words of all piyyutim and created major word initials for the complex compositions. The tradition to pay special attention to the beginning pages of yotsrot is attested in Ashkenazic mahzorim since the early thirteenth century, and it seems to have guided the scribe of this mahzor: The initial word of the yotser for the second day of Rosh ha-shanah is framed in a decorated panel, the initial word of the kol nidre is gilded. Other pages they might have contained decorated panels at the beginnings of other yotsrot are missing (first day of Rosh ha-shanah at the beginning) or were cut from the manuscript (second day of Sukkot, Shemini Atseret). The initial word of the yotser for the intermediate Sabbath of Sukkot (f. 210r) is peculiar in that a decorated panel was cut from the page and a parchment patch was inserted, reconstructing the text on both sides of the patch in a later but careful hand. Even though the manuscript does not contain illustrations, which can be found in many contemporary mahzorim, but used geometrical designs to decorate the panels for the initial words, it is likely that the missing pages from the beginning of yotsrot were cut out in order to be collected or displayed as examples of beautiful medieval manuscripts.