Can\'t understand this, trying to edit a unit

[Iced~Metal]

When you look at the entry for a crusader unit, such as Knights Templar, you'd notice that there are no building requirements, meaning that the unit cannot be built. So, in theory, if you just add a tag like:

{ Spearmaker }

Then they could be built, right? Wrong! The game would not load!

Anyone have any ideas??