att.source

att.source provides attributes for pointing to the source of a bibliographic reference. [3.3.3 Quotation 8.3.4 Writing]
Moduletei — The TEI Infrastructure
MembersegXML q quote writing
AttributesAttributes
source (pointer to a bibliographical source reference) provides a pointer to the bibliographical source from which a quotation or citation is drawn.
Status Optional
Datatype 1–∞ occurrences of 

<rng:ref name="data.pointer"/>
data.pointer
separated by whitespace
Values Must point to one or more bibliographic elements in the TEI header or elsewhere
Example
<p>
<!-- ... -->
As Willard McCarty (<bibl xml:id="mcc_2012">2012, p.2</bibl>)
tells us, <quote source="#mcc_2012">‘Collaboration’ is a
   problematic and should be a contested term.</quote>
<!-- ... -->
</p>
Example
<p>
<!-- ... -->
 <quote source="#chicago_15_ed">Grammatical theories
   are in flux, and the more we learn, the less we
   seem to know.</quote>
<!-- ... -->
</p>
<!-- ... -->
<bibl xml:id="chicago_15_ed">
 <title level="m">The Chicago Manual of Style</title>,
<edition>15th edition</edition>.
<pubPlace>Chicago</pubPlace>:
<publisher>University of Chicago Press</publisher>
(<date>2003</date>),
<biblScope unit="page">p.147</biblScope>.

</bibl>