I want to know the answer to the following question:
What does USB compliance specification prohibit?
All the background I'm provided with is that "However, USB compliance specification states that "use of a 'Y' cable (a cable with two A-plugs) is prohibited on any USB peripheral", meaning that "if a USB peripheral requires more power than allowed by the USB specification to which it is designed, then it must be self-powered."". Is that enough to answer the question?
Answer: yes