In Order to use the HTML Xtra while authoring, you need to
copy the Xtra files into the Xtras folder where the Director
application is installed.
On MacOS platforms (both 68k and PPC) simply copy the HTML.XTRA
file.
On Windows platforms you need to copy the HTML.X32 file.
16 Bit Windows versions are not supported anymore.
With the next launch of Director, the Xtra is automatically available.
To install the HTML Xtra for use by projectors, you need the above mentioned files inside the XTras folder, which needs to be in the same directory level as your projector. Now the Xtra is available automatically while the projector is launched.