Add documentation for ItemMapperSystem etc. (#9998)

Content.Shared/Storage/EntitySystems/SharedItemMapperSystem.cs

@@ -4,6 +4,11 @@ using Robust.Shared.Containers;
 
 namespace Content.Shared.Storage.EntitySystems
 {
+    /// <summary>
+    /// <c>ItemMapperSystem</c> is a system that on each initialization, insertion, removal of an entity from
+    /// given <see cref="ItemMapperComponent"/> (with appropriate storage attached) will check each stored item to see
+    /// if its tags/component, and overall quantity match <see cref="ItemMapperComponent.MapLayers"/>.
+    /// </summary>
     [UsedImplicitly]
     public abstract class SharedItemMapperSystem : EntitySystem
     {
@@ -45,6 +50,17 @@ namespace Content.Shared.Storage.EntitySystems
             }
         }
 
+        /// <summary>
+        /// Method that iterates over storage of the entity in <paramref name="msg"/> and sets <paramref name="containedLayers"/> according to
+        /// <paramref name="itemMapper"/> definition. It will have O(n*m) time behavior (n - number of entities in container, and m - number of
+        /// definitions in <paramref name="containedLayers"/>.
+        /// </summary>
+        /// <param name="msg">event with EntityUid used to search the storage</param>
+        /// <param name="itemMapper">component that contains definition used to map <see cref="Content.Shared.Whitelist.EntityWhitelist">whitelist</see> in
+        /// <c>mapLayers</c> to string.
+        /// </param>
+        /// <param name="containedLayers">list of <paramref name="itemMapper"/> layers that should be visible</param>
+        /// <returns>false if <c>msg.Container.Owner</c> is not a storage, true otherwise.</returns>
         protected abstract bool TryGetLayers(ContainerModifiedMessage msg,
             ItemMapperComponent itemMapper,
             out IReadOnlyList<string> containedLayers);