Critical apparatus is a standard feature of scholarly editions in which variant readings and related comments are presented to readers as a compressed list immediately following the text, organized by line numbers therein.
Form and content of the apparatus varies from one discipline to another in the humanities. In manuscript studies and literary philology, the app. crit. is generally differentiated from a separate line-by-line commentary, and is devoted narrowly to the documentation of variant readings found in extant witnesses. In epigraphic and papyrological practice, where there is normally only one ancient witness to a text, the apparatus regularly treats divergeant or erroneous readings published by prior editors, alternative restorations and emendations, and comments on form and appearance (e.g., transposition of letters) that cannot be clearly represented in the text itself. Epigraphers and papyrologists often also include a commentary (line-by-line or otherwise) in which more extended discussion of the text and its interpretation and historical significance can be addressed.
EpiDoc provides two methods of encoding the sort of information that is traditionally placed in the critical apparatus. The in-line approach makes use of tags placed directly in the text, which can then be interpreted during post-processing for display in a line-by-line form. In the external approach, the apparatus is encoded explicitly in a separate <div type="apparatus"> element. The individual apparatus entries in such an external division are tied back to the text using standard TEI linking attributes.
Specific guidance for each approach is provided in its own section as follows: