A constraint string is a string literal, the contents of which are composed of two parts.
The contents of the constraint string are:
10.4.1 Constraint modifiers.
10.4.2 Constraint codes.
10.4.3 Constraint codes common to AArch32 state and AArch64 state.
10.4.4 Constraint codes for AArch32 state.
10.4.5 Constraint codes for AArch64 state.
10.4.6 Using multiple alternative operand constraints.