Help+Manual Help stores your projects as a collection of plain text XML files, the code of which looks a little like HTML. You don't need to know anything at all about XML to use the program.
If you are using the Professional or Server version of Help+Manual you can save your project in single-file compressed mode (HMXZ) or uncompressed XML mode (HMXP). Single-file mode saves all your project files in a single compressed file with the extension .hmxz. Uncompressed mode saves your project as a collection of files and folders with a project file with the extension .hmxp. Uncompressed XML projects must always be saved in an empty folder.
The uncompressed XML format (.hmxp) is only supported in the Professional and Server versions of Help+Manual. The Basic version can only save in the compressed single-file format (.hmxz).