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

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

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

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