When creating a new report, one can create a new report group. Since its code will be used in tab id attribute, it should be tested to contain only ASCII chars (and no space) : [a-zA-Z0-9_-]
Also looks like an id must start with a letter. Even if it is under debate for HTML5, we have a library reporting this issue. See https://stackoverflow.com/questions/5672903/can-i-have-an-element-with-an-id-that-starts-with-a-number
*** Bug 35580 has been marked as a duplicate of this bug. ***