One of the 508 compliance rules are that all OBJECT tags should contain element content. I'm not familiar with OBJECT tags or anything, but what should the content usually be? I noticed if I just put any string within the OBJECT tags I seem to pass the 508 test.
Is it acceptable to put anything within the OBJECT tags to make this pass verification? Can I just put "useless string"? What effect does the content have?
The content is for fallback in the case that the browser for any reason cannot display the object. Think of it as like the alt attribute for <img> elements. An automated checker can't verify that you are putting something sensible in, only that you've put something in.
It's your responsibility to make that content sensible. It should provide the best possible equivalent in text (or other HTML) that you can provide that conveys the same information as would have been conveyed by the object had it been displayable.
The content should provide information equivalent to the embedded object.
Using an useless string will not make it 508 compliant. Thus, that wouldn't be acceptable if your goal is 508 compliance. Your automated test may report a pass, but it's not really compliant unless it has real content.
The effect of this alternate content? When a disabled person visits the website and their assistive software cannot process the embedded object, the software falls back to the alternate content. Let's say you embed a Flash presentation in the page. When a blind person visits the site with a screen reading software, the screen reading software might not be able to parse the Flash movie. Instead, it reads out the text that is in the alternate content.