HTML
There currently is only one option to set on the HTML panel: you can set the Creator type of exported HTML files. The Mac OS uses a unique code (called the Creator type) to identify which program created a file. (That's how it knows to open Simpletext when you click on a Simpletext document.)
Since Z-Write can generate HTML files, it can be helpful to have Z-Write make the files match the Creator of an Internet program of your choosing. This could be your preferred web browser, such as Internet Explorer, or perhaps an HTML editor like Adobe GoLive.
Z-Write knows the Creator codes of several popular programs by default and you can choose them from the popup menu. You may also choose the "Select an HTML Editor..." option to choose any application installed on your computer. Once you have set this setting, Z-Write will generate HTML that can be opened in that application simply by double-clicking on them in the Finder.