PS 9.2 - Tax update 20E Eugene OR tax

We are looking for more information on the Eugene OR tax.

We are trying to answer these questions.

1. Is the tax rate based on their job record? Rate x standard hours? 
2. Is the tax rate actually based on their regular hours x rate on each check each week? This is what the document seems to be stating.
3. If #2 is how it actually works, what defines “regular hours”. Do that included premiums, vacation, sick, holiday, etc?
4. Is it looking at Earnings program table to determine “regular hours”?
5. Document states all earnings are subject to the tax. If a bonus is paid on an separate check, or off cycle, how would it calculated a rate since there would be no regulars on that check.