What is "headerdoc"

HeaderDoc is a documentation generator developed and maintained by Apple Inc. Using specially commented source code files as input, HeaderDoc generates documentation for the code in HTML or XML format. Syntax for HeaderDoc comment tags is largely similar to, and as of HeaderDoc version 8, supportive of Javadoc tags. HeaderDoc 8.7 and later also provides partial support for many Doxygen tags (@ form only, and must conform to HeaderDoc tag ordering rules). Apple's HeaderDoc project is free, open source software distributed under the Apple Public Source License.