The heterogeneous nature and historical significance of this letter collection necessitate careful explanation and contextualisation. To address this need, the <hi xmlns="http://www.tei-c.org/ns/1.0" rend="italic">Heinrich Bullinger Briefwechsel</hi> (HBBW) (Gäbler et al., 1973–2024) was established. Initiated in 1973, this classical edition project<ref xmlns="http://www.tei-c.org/ns/1.0" n="2" target="ftn2" /> has processed over 3,100 letters to date. Each volume features an extensive preface that contextualises the letters within their historical period, followed by the letters themselves. Each letter is presented with detailed metadata (author, recipient, location, date), manuscript information, and relevant secondary literature. The letters are then summarised (DE <hi xmlns="http://www.tei-c.org/ns/1.0" rend="italic">Regest</hi>), transcribed, and annotated with footnotes. Under the project <hi xmlns="http://www.tei-c.org/ns/1.0" rend="italic">Bullinger Digital</hi> the entire edition has been made available in machine readable format (TEI/XML)<ref xmlns="http://www.tei-c.org/ns/1.0" n="3" target="ftn3" />. Figure 1 shows an example of an edited letter from volume 6 of the edition in its digital representation including the footnote apparatus.