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Instruction format in documentation ARM-v7-A

Hi. This is the first time to ask questions in this forum. Hope this is the right place to reach you and get help.

I refer to the documentation ARMv7-A and ARMv7-R edition

I don't understand the brackets() in the instruction details.

 For example, the pic above is the description of  instruction MSR. I noticed that the bit index from 12 to 15 is 1 but with a bracket. I may loss the definition of this kind of bracket. I am sorry that I didn't find it in the documentation. Who can tell me what is the bracket used for. Are there any differences if a bit is inside a bracket or not? Many Thanks