[1] ALTO: Technical Metadata for Layout and Text Objects (Standards, Library of Congress) (2016-06-16 23:05:30 +09:00) <https://www.loc.gov/standards/alto/>

[2] altoxml/schema: ALTO XML schema - latest and all former versions (2017-07-09 00:15:06 +09:00) <https://github.com/altoxml/schema>

[3] Home · altoxml/documentation Wiki (2017-07-09 00:15:20 +09:00) <https://github.com/altoxml/documentation/wiki>

[4] ALTO (XML) - Wikipedia (2017-06-23 21:09:49 +09:00) <https://en.wikipedia.org/wiki/ALTO_(XML)>