Define "edge of the page" for a web page where the user can resize the window to any size.

The solution is to pick a length where you want to break the string. You can insert spaces to allow the browser to do the wrapping. Unluckily, the spaces will be visible if the browser doesn't wrap right there. Or you can insert <br> tags to force a break.

One experiment you might try is using a zero-width space character (&#8203;) and see if browsers support it correctly. It should be considered whitespace and cause word wrap, but not show when in the middle of a line. Try inserting one every 20 characters or so.