From The Battle for Wesnoth Wiki
the [units] tag
This tag is a top level WML tag which is in game.cfg. It defines the set of all units in Wesnoth.
The following subtags are recognized:
- [unit] describes one unit type. See UnitWML for syntax.
- [trait] describes a global trait.
All races with the attribute ignore_global_traits=no will have this trait. See [trait] below for syntax.
- [movetype] used to make shortcuts to describe units with similar terrain handicaps. Units from the same advancement tree should generally have the same movetype.
- name an ID for this movetype. Units with the attribute movetype=name will be assigned this movetype.
- flies either 'true' or 'false'(default). A unit with flies=true does not have its image's height adjusted for different terrains.
- [movement_costs] describes how fast the unit moves on different terrains. The attribute terrain=speed means that the unit will need to use speed move points to move onto the terrain with name=terrain (see TerrainWML).
- [defense] describes how likely the unit is to be hit on different terrains. The attribute terrain=defense means that the unit will be hit defense percent of the time in the terrain with name=terrain.
- [resistance] describes how much damage the unit takes from different types of attacks. The attribute type=resistance makes the unit resist 100-resistance percent of damage from attacks with type=type.
- [race] is used to make shortcuts to describe units with similar names. Units from the same advancement tree should generally have the same race. Also, units with the same race should generally be recruitable by the same sides/factions.
- name an ID for this race. Units with the attribute race=name will be assigned this race.
- male_names, female_names lists of names (i.e. non-translatable strings). They are inputted into the Markov name generator to generate random names. male_names describes units with gender=male; female_names describes units with gender=female.
- markov_chain_size (default 2) number of letters per "syllable". "Syllables" are groupings of names that the Markov name generator uses to determine names. It does this by running a probability algorithm to guess from the name list which syllables fit well together, which can start or end a name, etc.
- not_living 'yes' or 'no'(default). Units with not_living=yes cannot be poisoned, drained from, or plagued (see AbilitiesWML).
- num_traits is the number of non-repeating traits each unit of this race can be assigned.
- ignore_global_traits 'yes' or 'no'(default). Determines whether global traits (see [traits] above) are applied.
- [trait] describes a trait for this race. Has attributes id internationalization key(?), name text displayed in the status of unit with the trait, and tag [effect], described in EffectWML.