Extension for WebApplication Extensibility point in the WiX XML Schema. Schema extensions can register additional elements at this point in the schema. Usually a Property that resolves to short file name path. Extension being registered. Do not prefix with a '.' (e.g. you should use "html", not ".html"). To register for all extensions, use Extension="*". To register a wildcard application map (which handles all requests, even those for directories or files with no extension) omit the Extension attribute completely. Extensibility point in the WiX XML Schema. Schema extensions can register additional attributes at this point in the schema.