Autocomments are fragments of the edit summary (which is commonly referenced within the codebase as "comment") inside C-style comment markers. For example, the edit summary
/* foo */ bar /* baz */ boom contains two autocomments,
baz. Autocomments are mainly used for specifying which section was edited; the default comment formatter behavior turns the autocomment into a link to the section with the same name.
The FormatAutocomments hook can be used to customize autocomment handling; some extensions use it to generate multilingual comments by putting the i18n message key and parameters in an autocomment. For example, adding a sitelink to French Wikipedia on Wikidata would result in an edit summary of
/* wbsetsitelink-add:1|frwiki */ which the hook would replace with the output of
wfMessage( 'wbsetsitelink-add', 1, 'frwiki' ).
External tools which want to display edit summaries the same way they are displayed in MediaWiki can use the
parsedcomment property of the various revision-related APIs.