Micro AIs
From The Battle for Wesnoth Wiki
The add-on AI Modification Demos contains a number of so-called Micro AIs (well, currently there's one, but the goal is to add more). Mirco AIs add specific functionalities to a side's AI and can be added to a scenario easily using only a few lines of WML code. Adding (or deleting) the Micro AI is done via the [micro_ai] tag, which also lets the campaign designer configure the AI behavior to the specific need of the scenario.
Note that the current Micro AIs are written for Wesnoth 1.10 in order to increase the number of people that can give feedback on the AI behavior itself. They should work in Wesnoth 1.11 as well (please report if you find that they don't), but they don't make use of the new features (yet).