This method is used to tell which errors you expect to get.
Expected errors are always returned with error mode
PEAR_ERROR_RETURN.
Expected error codes are stored in a stack,
and this method pushes a new element onto it. The list of
expected errors are in effect until they are popped off the
stack with the popExpect() method.
Parameter
mixed $errorCode -
the expected
PEAR_Error error code or
an array of error codes. If set to '*'
every error is expected.