Codicology is the study of the manuscript book as a physical object, its gathering structure, the ruling pattern scored into the parchment or paper, the pricking marks that guided that ruling, the ink and pigments used and the binding that holds the whole together, independent of what the text written on it says. Manuscript specialists had practiced elements of the method for generations, but the French scholar Alphonse Dain gave the discipline its name and its first systematic statement in his 1949 book Les manuscrits, arguing that a manuscript's physical construction was itself primary evidence for its date, origin and use, deserving study in its own right rather than as mere support for editing its text.
The atlas draws on codicology wherever a scripture or liturgical book's claimed date or place of origin needs a check independent of its contents. Two manuscripts can carry the identical text while differing sharply in construction, and codicological evidence, the quire structure of a particular scriptorium, a regional ruling pattern, a datable binding style, can place a manuscript in a specific time and place even when its colophon is missing, forged or simply silent. Where a tradition dates one of its own sacred manuscripts by tradition alone, codicological findings are recorded as the independent check.