PIC32 Special Function Registers (SFRs) can be accessed like ordinary variables in C but there can be read-modify-write problems associated with code that wants to change individual bits in these registers.
To get around this problem, virtually all registers have an alternate register set, using the primary register name appended with SET, CLR, or INV. Each of these can be assigned a value in the usual way, but this write operation will instead set, clear, or toggle (respectively) bits within the primary register. Where a bit in the written value is one, this will trigger the appropriate operation in the primary register at the corresponding bit position. This is a single access and therefore solves issues with read, modify, write operations.