The Book of Struggles gives a complete mechanism for handling character to character conflicts. However its possible to have more detailed rule extensions for specific situations, and extended examples of using the struggle rules in those specific situations. Hence the value of the Toolkits.
The Combat Toolkit gives examples of the struggle mechanism in use for Brawling, Close Combat, Firefights and Rearguard Actions. It explains conditions that might be pertinent and complication examples.
In addition to the combat situations being fleshed out it provides some extended mechanics for handling injury and death, natural healing and medical intervention. The injury levels are Minor, Serious, Incapacitated, Critical and Mortal. Each injury level has a natural healing cycle during which the injury may worsen or improve. The medical interventions are defined as First Aid, Field Care, Hospital Care, and Surgery. Characters use their related aptitudes to carry out the interventions and if done well will improve the healing process.
This extension can add a mild layer of complexity onto combat struggles. The play testing is focusing on ensuring that these things hang together well with the narrative style of play and can be operated smoothly during the session when used.