From [OLPC News (2006-10-14)|http://laptop.media.mit.edu/laptopnews.nsf/2e76a5a80bc36cbf85256cd700545fa5/2cc25a58f0d1a6e8852572070033befc?OpenDocument ]:

The OLPC document format spec rev2 has support for block macros,
granular tables of contents, and layout hinting. The format is named
“Crossmark,” and is believed to be highly suitable for (collaborative) book
writing and editing and use as an e-book format.