In WPT perform_actions/invalid.py, we are expected to check if the parameter value for the webdriver actions must be in boundary of ECMA safe integer.

One example is https://github.com/web-platform-tests/wpt/blob/master/webdriver/tests/classic/perform_actions/invalid.py#L237-L250

I can't find in spec where to check for this safe number. Is the spec not complete or is it implied somewhere and I didn't catch it? Thanks