Multiproduce is a method of letting multiple units be produced with one produce command (at one cost for all the units). Multiproduce is only available in GAE 0.4.x plus. If a production command is told to multiproduce, it can only produce that number, never less. So if multiproducing 3 swordman, they have to be done in groups of 3, and you can't produce just one unless a separate command is made for that.
<command> <type value="produce"/> <name value="hire_gunner_squad" tip="gunner_info"/> <image path="../gunner/images/canoneer.bmp" /> <unit-requirements /> <upgrade-requirements /> <produce-skill value="produce_skill"/> <produced-unit name="gunner" number="3"/> </command>
The only change here is the number value in the produced-unit element. Everything else is the same as a normal produce command.