The election form and the plan definition of compensation should coordinate. I would imagine that a good 401(k) would define earnings in terms of taxable compensation plus salary deferrals (or prior to salary deferrals).
The intention in your example surely is that the person, who would, but for the salary deferrals, receive $10,000 and who elects to defer 10% would in fact wind up deferring $1,000, right? Make the plan document, the intention and actual administration all match up.
Are there 401(k) plans out there (I do not work on 401(k) plans) that do NOT include salary deferrals in the definition of earnings? At best, if deferrals are not counted in the definition of compensation, don't you wind up with some kind of recursive mess? Let's see: Pay before deferrals is $10,000, elects to defer 10%. That would be $1,000, but then earnings =$9,000, so 10% = $900, but then pay before deferrals is $9,100 so deferral is $910, but wait, then pay = $9,090 and deferral = aw forget it. Just make sure that the definition of pay includes deferrals.