@ Naim - well done with the photos from the owners manual. Up to 10% ethanol seems OK, but I sense some caution about methanol.
@ Ferrix - the Malaysian model is probably set for 91 octane. However as the CBR250R is intended to be sold around the world, in different markets it will have different settings.
It used to be that lower compression ratios were used for lower octane. Timing settings were different too.. My first car was a Morris Oxford with the low 7.5:1 compression ratio and could use standard petrol, which at the time in NZ was 79 octane, as I recall. The standard engine in the UK, where higher octane petrol was available, was 8.5:1.
Now it is all done with the electronics.
@ basil - From what I have read; there is no advantage using higher octane petrol than specified; it is a waste of money.
Using lower than specified octane will result in decreased performance, and increased chance of engine knock, or "pinking". If you take it easy you should have no problems, but it is best to use the recommended octane if you can.