SpiderBasic

The behavior of ExamineMouse() is a little strange. From the first click on the mouse is captured and you get a warning in the browser. I guess even for the most games this is not what you want - you simply want to keep the systems mouse cursor.
It would be good if there would be a way to tell spiderbasic to not capture the mouse cursor. At first I thought ReleaseMouse(1) would do the trick - but that doesn't work.

Edit:

spider.mouse.locked = true; in the index.html in a script block in the header does the trick - but a native support would be great

When the mouse is locked, it is also hidden which is needed for many games, so you can have your own cursor, and the mouse won't get outside the gaming area. But adding a flag can be nice way to handle both cases, that's right.