A register holds the number of parameters. IX points to each parameter. IX+0/IX+1 is the last parameter. This happens because each parameter in order is pushed onto the stack and IX then points to the last parameter pushed. Each parameter is a 16-bit value.
If a parameter is a string, then IX holds the 16-bit value is an address of a "the string descriptor which point to a 3 byte block". The first byte of the string descriptor is the length. The next 2 bytes are an address that point to the string in memory.
With the help of the variable container "@" it is also possible to get a result from an invoked mc-code back to basic.