Markup format used in ZoPe?, ZWiki uses it with some wiki-specific stuff added, like WikiName''s. It provides for extensive formatting using clean, intuitive rules, so that the text content is very easy to read, write, and edit in the original form. See TextFormattingRules for the whole scoop on ZWiki formatting. The links below include some further details on StructuredText, itself.
Here are the StructuredTextRules, from the source.
Here is a structured text HowTo on zope.org.
See also ZWikiWeb:StructuredText