prior to starting a match, the player selects one of several perks (or classes) that represent basic combat classes (e.g. field medic, commando, support). each perk has various skill boosts (e.g. better damage with specific weapons, healing other characters, welding doors more effectively) that are unavailable to other perks. in the meta-game, players earn experience points for each of their perks by doing actions related to those perks, for example, healing other players will gain field medic experience points. the player can also acquire those same experience points when they are not using the appropriate perk. experience points are most easily earned by using weapons specific to the class, such as explosive weapons for the demolitions class. each level gained boosts the perk's base skill numbers. for every five levels gained, the player is able to select one of two specific skills unlocked for the respective perk. these skills include a mix of passive and active abilities, including some that can benefit other team members. players can also configure their playable character through a number of pre-made personas and options for various clothing and accessories, but these customizations are purely cosmetic with no impact on gameplay mechanics.