For latest documentation and authoring information please see the MVP site mshelpwiki.helpmvp.com
AP Help is the help system used by Windows Vista (codename: Longhorn) Operating System. It is used by Windows Vista OS and OEM help. AP Help is an extension of MS Help 2 (help for VS 2002/2003/2005/2008) and introduces MAML, an XML based help mark up language. The Help SDK compiles to a .h1s file. AP Help remains for Windows Vista OS and OEM help only.
Help for VS 2010 (HV 1.0), VS 2012 and Windows 8 OS (HV 2.0). Help source is simply zipped to a .mshc help file. Compilation (ripping) occurs when help is installed although help can now also be run standalone separate from VS Help system. Windows 8 help viewer remains undocumented.