StandardSideFilter
From The Battle for Wesnoth Wiki
From FilterWML, this is the standard way of filtering on sides. The following attributes and sub-tags are permitted:
- side: filter matches only if side number is contained in a comma-separated list. 'all' matches all sides.
- [has_unit]: filter matches only if side controls a unit matched by this StandardUnitFilter
Also, [and], [or], and [not] subfilters are supported.