DEFINE HSER_CLROERR 1 ; how do I work? am I taxing performance heavily?

How does DEFINE HSER_CLROERR 1 work?
Does it turn on interrupts and toggle CREN & SPEN when the recieve buffer interrupt is thrown?
or simply toggle CREN & SPEN bits whenever anything hits the receive buffer(OERR bit? or RCIF transfer bit?) ?
...
also, is there anyway for me to see what 'DEFINES' are coded to do?

thanks in advance! :)