The order property is a simple string. When the game needs to sort prototypes (of the same type), it looks at their order properties and sorts those alphabetically. A prototype with an order string of "a" will be listed before other prototypes with order string "b" or "c". The "-" or "[]" structures that can be found in vanilla order strings do *not* have any special meaning.
The alphabetical sorting uses lexicographical comparison to determine if a given prototype is shown before or after another. If the order strings are equal then the game falls back to comparing the prototype names to determine order.
string