att.witnessed supplies the attribute used to identify the witnesses supporting a particular reading in a critical apparatus. [12.1 The Apparatus Entry, Readings, and Witnesses]
Moduletextcrit — Critical Apparatus
Memberslem rdg
wit(witness or witnesses) contains a space-delimited list of one or more pointers indicating the witnesses which attest to a given reading.
Status Optional
Datatype 1–∞ occurrences of teidata.pointer separated by whitespace

If the apparatus contains readings only for a single witness, this attribute may be consistently omitted.

This attribute may occur both within an apparatus gathering variant readings in the transcription of an individual witness and within an apparatus gathering readings from different witnesses.

Additional descriptions or alternative versions of the sigla referenced may be supplied as the content of a child wit element.