This section of the EpiDoc Guidelines provides direction for encoding the date of origin of the text (or in some cases, of the object or some other feature, decoration, or reuse of it), whether the result of the editor's analysis or an explicit, internal date. Guidance is also provided on recording possible ranges of dates, degrees of precision and dating criteria.
The date of orgin of the text (or object, if different) should be recorded in an origDate element in the <origin> section of the manuscript description area (see the general section on provenance for context). If different dates need to be recorded for text and object, different texts on the same support, or different interventions in the same text, the origDate may be repeated, or the entire <history> may be embedded in multiple <msPart>s.
It is generally recommended to encode the dating information in numerical form, following the proleptic Julian calendar, using the att.datable.custom attributes on the origDate element. These "custom" date attributes are required because the default dating system assumed by the basic TEI date attributes (att.datable) is the Gregorian calendar. Moreover, therefore, the dating element should always carry a datingMethod attribute pointing to a <calendar> element in the header--or to an external authority for the Julian calendar, such as http://en.wikipedia.org/wiki/Julian_calendar.
A specific date, whether a single day, month, or year in the Julian calendar, can be expressed using the when-custom attribute, which should be laid out in the same form as an ISO 8601/W3C date (albeit in the Julian, not Gregorian calendar). In other words:
A date within a range (such as the reign of an emperor, or a century for e.g. palaeographically dated text) should be encoded using the notBefore-custom and notAfter-custom attributes, marking the beginning and end of the possible span of dates. The date formats of these attributes are the same as for <when-custom>.
This example encodes a simple Julian date:
This example encodes a date range, again in Julian calendar:
Not all texts are dated confidently to a specific year or firm span of years. If a date given is flagged explicitly as less certain than usual (for example, either with a "?" or a formulation such as "just possibly") the origDate may be given a cert attribute with a value of "low". If a date is flagged as approximate (which is different from being uncertain; often written "circa", "ca." or "c.") origDate should be given an precision with a value of low. If a date range is specified (with notBefore-custom and notAfter-custom) whose start and end points are essentially arbitrary, such as a century or half-century for a palaeographical date, then a precision of "medium" should be given, to indicate that the start and end-points are both notional.
In a few cases, a text may be dated within a span of dates with a notional end-point but a firm terminus post quem. To record this in XML, a <precision> element may be placed inside the origDate to point to whichever of the attributes represents the less concrete end-point. (See third example below.)
... @evidence, suggest typology, example values ...
Cf EpiDoc dating criteria vocabulary (Google Spreadsheet)