[1] ALTO: Technical Metadata for Layout and Text Objects (Standards, Library of Congress) () <https://www.loc.gov/standards/alto/>
[2] altoxml/schema: ALTO XML schema - latest and all former versions () <https://github.com/altoxml/schema>
[3] Home · altoxml/documentation Wiki () <https://github.com/altoxml/documentation/wiki>
[4] ALTO (XML) - Wikipedia () <https://en.wikipedia.org/wiki/ALTO_(XML)>