SAPI stands for "Server Application Programming Interface". It is the mechanism that controls the interaction between the "outside world" and the PHP/Zend engine. it is the direct module interface to ...

if (sapi_module.send_headers) { retval = sapi_module.send_headers(&SG(sapi_headers)); } else { retval = SAPI_HEADER_DO_SEND; } switch (retval) { case SAPI_HEADER_DO ...