"This is just for HTML but is there a list of all such command capabilities, including Javascript and/or PHP, as well as HTML?"

It doesn't matter what language(s) are on the page and/or involved in generating the page. The end result must always be an HTTP request for a "special" URL like the ones you mention above.

All the special URLs are documented somewhere but right this second I can't find them. Off the top of my head:

In all of the following, "C" represents the camera number of the cam you want to affect. As you've already discovered, the first (only?) cam is 0 not 1.

Incremental moves of PT:
X and Y are "step sizes" - experiment with values for your cam.

homeC-0
leftC-X
rightC-X
upC-Y
downC-Y

Incremental Zoom:
Z is the zoom increment, usually a small number like 0.1 or 0.2

zoomC-Z {zooms in}
zoomC--Z {zooms out}

Absolute positioning:
X and Y are absolute locations on a -100 to 100 coordinate system.

posC-X,Y {where X and Y are both positive)
posC--X,-Y {where X and Y are both negative)
posC--X,Y {where X is negative and Y positive)
posC-X,-Y {where X is positive and Y negative)

You can also do absolute zoom in conjunction with the pos command by adding zoom value (1.0 to Zoom Max) to any of the above. Like this:

posC-X,Y,Z

For example, pos0-50,25,1.5

Or just go to my site and "steal" my page source - it uses most of the above techniques. My site is "Control Stuff" on the Camera List here on this site.