Text Encoding Inititative (TEI or TEI-XML)
TEI Guidelines for Electronic Text Encoding and Interchange: https://www.tei-c.org/release/doc/tei-p5-doc/en/html/index.html
The Journal of the Text Encoding Initiative (JTEI): https://journals.openedition.org/jtei/
Comic Book Markup Language (CBML)
About: http://dcl.ils.indiana.edu/cbml/
Article about CBML: http://www.digitalhumanities.org/dhq/vol/6/1/000117/000117.html