diff --git a/.componentsignore b/.componentsignore
index 094a031f5..7c399b333 100644
--- a/.componentsignore
+++ b/.componentsignore
@@ -24,5 +24,6 @@
   "VariableBindings",
   "UnionHandler",
   "WinstonLogger",
+  "WrappedSetMultiMap",
   "YargsOptions"
 ]
diff --git a/src/index.ts b/src/index.ts
index 47fd5ea13..98550f716 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -438,6 +438,8 @@ export * from './util/locking/VoidLocker';
 
 // Util/Map
 export * from './util/map/HashMap';
+export * from './util/map/SetMultiMap';
+export * from './util/map/WrappedSetMultiMap';
 
 // Util/Templates
 export * from './util/templates/ChainedTemplateEngine';
diff --git a/src/util/map/SetMultiMap.ts b/src/util/map/SetMultiMap.ts
new file mode 100644
index 000000000..a0a15f30e
--- /dev/null
+++ b/src/util/map/SetMultiMap.ts
@@ -0,0 +1,59 @@
+/**
+ * A SetMultiMap is a Map where a single key can have multiple unique values.
+ * Deleting a key removes all bindings with this key from the Map.
+ * Setting a value for a key replaces all previous bindings with this key.
+ * Using an empty Set when calling the `set` function is the same as deleting that key.
+ */
+export interface SetMultiMap<TKey, TVal> extends Map<TKey, TVal | ReadonlySet<TVal>> {
+  /**
+   * Returns all values stored for the given key.
+   * Returns `undefined` if there are no values for this key.
+   */
+  get: (key: TKey) => ReadonlySet<TVal> | undefined;
+  /**
+   * Returns true if this key/value binding exists in the Map.
+   */
+  hasEntry: (key: TKey, value: TVal) => boolean;
+  /**
+   * Adds the given key/value binding to the Map.
+   */
+  add: (key: TKey, value: TVal | ReadonlySet<TVal>) => this;
+  /**
+   * Deletes the given key/value binding from the Map.
+   */
+  deleteEntry: (key: TKey, value: TVal) => boolean;
+
+  /**
+   * Returns a Readonly {@link Map} representation of this Map.
+   */
+  asMap: () => ReadonlyMap<TKey, ReadonlySet<TVal>>;
+
+  /**
+   * Iterates over all key/value bindings in this Map.
+   */
+  [Symbol.iterator]: () => IterableIterator<[TKey, TVal]>;
+  /**
+   * Iterates over all key/value bindings in this Map.
+   */
+  entries: () => IterableIterator<[TKey, TVal]>;
+  /**
+   * Iterates over all distinct keys in this Map, together with a {@link Set} of their values.
+   */
+  entrySets: () => IterableIterator<[TKey, ReadonlySet<TVal>]>;
+  /**
+   * Iterates over all distinct keys in this Map.
+   */
+  distinctKeys: () => IterableIterator<TKey>;
+  /**
+   * Iterates over all values in this Map.
+   */
+  values: () => IterableIterator<TVal>;
+  /**
+   * Iterates over all distinct keys and returns their {@link Set} of values.
+   */
+  valueSets: () => IterableIterator<ReadonlySet<TVal>>;
+  /**
+   * Loops over all key/value bindings.
+   */
+  forEach: (callbackfn: (value: TVal, key: TKey, map: SetMultiMap<TKey, TVal>) => void, thisArg?: any) => void;
+}
diff --git a/src/util/map/WrappedSetMultiMap.ts b/src/util/map/WrappedSetMultiMap.ts
new file mode 100644
index 000000000..7d19687da
--- /dev/null
+++ b/src/util/map/WrappedSetMultiMap.ts
@@ -0,0 +1,149 @@
+import type { SetMultiMap } from './SetMultiMap';
+
+/**
+ * A {@link SetMultiMap} that uses an internal Map based on the provided constructor.
+ *
+ * In case no input constructor is provided, the default Map implementation will be used.
+ *
+ * It is required that the value type of this map is not Set or any extension of Set,
+ * otherwise the `set` and `add` functions wil break.
+ */
+export class WrappedSetMultiMap<TKey, TVal> implements SetMultiMap<TKey, TVal> {
+  private count: number;
+  private readonly map: Map<TKey, Set<TVal>>;
+
+  /**
+   * @param mapConstructor - Will be used to instantiate the internal Map.
+   * @param iterable - Entries to add to the map.
+   */
+  public constructor(mapConstructor: new() => Map<any, any> = Map,
+    iterable?: Iterable<readonly [TKey, TVal | ReadonlySet<TVal>]>) {
+    this.map = new mapConstructor();
+    this.count = 0;
+
+    if (iterable) {
+      for (const [ key, val ] of iterable) {
+        this.add(key, val);
+      }
+    }
+  }
+
+  public has(key: TKey): boolean {
+    return this.map.has(key);
+  }
+
+  public hasEntry(key: TKey, value: TVal): boolean {
+    return Boolean(this.map.get(key)?.has(value));
+  }
+
+  public get(key: TKey): ReadonlySet<TVal> | undefined {
+    return this.map.get(key);
+  }
+
+  public set(key: TKey, value: ReadonlySet<TVal> | TVal): this {
+    const setCount = this.get(key)?.size ?? 0;
+    const set = value instanceof Set ? new Set(value) : new Set([ value ]);
+    this.count += set.size - setCount;
+    if (set.size > 0) {
+      this.map.set(key, set);
+    } else {
+      this.map.delete(key);
+    }
+
+    return this;
+  }
+
+  public add(key: TKey, value: TVal | ReadonlySet<TVal>): this {
+    const it = value instanceof Set ? value : [ value ];
+    let set = this.map.get(key);
+    if (set) {
+      const originalCount = set.size;
+      for (const entry of it) {
+        set.add(entry);
+      }
+      this.count += set.size - originalCount;
+    } else {
+      set = new Set(it);
+      this.count += set.size;
+      this.map.set(key, set);
+    }
+
+    return this;
+  }
+
+  public delete(key: TKey): boolean {
+    const setCount = this.get(key)?.size ?? 0;
+    const existed = this.map.delete(key);
+    this.count -= setCount;
+    return existed;
+  }
+
+  public deleteEntry(key: TKey, value: TVal): boolean {
+    const set = this.map.get(key);
+    if (set?.delete(value)) {
+      this.count -= 1;
+      if (set.size === 0) {
+        this.map.delete(key);
+      }
+      return true;
+    }
+    return false;
+  }
+
+  public clear(): void {
+    this.map.clear();
+    this.count = 0;
+  }
+
+  public asMap(): ReadonlyMap<TKey, ReadonlySet<TVal>> {
+    return this.map;
+  }
+
+  public [Symbol.iterator](): IterableIterator<[TKey, TVal]> {
+    return this.entries();
+  }
+
+  public* entries(): IterableIterator<[TKey, TVal]> {
+    for (const [ key, set ] of this.map) {
+      for (const value of set) {
+        yield [ key, value ];
+      }
+    }
+  }
+
+  public* entrySets(): IterableIterator<[TKey, ReadonlySet<TVal>]> {
+    yield* this.map.entries();
+  }
+
+  public* keys(): IterableIterator<TKey> {
+    for (const [ key ] of this.entries()) {
+      yield key;
+    }
+  }
+
+  public distinctKeys(): IterableIterator<TKey> {
+    return this.map.keys();
+  }
+
+  public* values(): IterableIterator<TVal> {
+    for (const [ , value ] of this.entries()) {
+      yield value;
+    }
+  }
+
+  public valueSets(): IterableIterator<ReadonlySet<TVal>> {
+    return this.map.values();
+  }
+
+  public forEach(callbackfn: (value: TVal, key: TKey, map: SetMultiMap<TKey, TVal>) => void, thisArg?: any): void {
+    for (const [ key, value ] of this) {
+      callbackfn.bind(thisArg)(value, key, this);
+    }
+  }
+
+  public get size(): number {
+    return this.count;
+  }
+
+  public readonly [Symbol.toStringTag] = 'WrappedSetMultiMap';
+}
diff --git a/test/unit/util/map/WrappedSetMultiMap.test.ts b/test/unit/util/map/WrappedSetMultiMap.test.ts
new file mode 100644
index 000000000..7945ad477
--- /dev/null
+++ b/test/unit/util/map/WrappedSetMultiMap.test.ts
@@ -0,0 +1,164 @@
+import { WrappedSetMultiMap } from '../../../../src/util/map/WrappedSetMultiMap';
+
+describe('A WrappedSetMultiMap', (): void => {
+  const key = 'key';
+  let map: WrappedSetMultiMap<string, number>;
+
+  beforeEach(async(): Promise<void> => {
+    map = new WrappedSetMultiMap();
+  });
+
+  it('can set values and check their existence.', async(): Promise<void> => {
+    expect(map.set(key, 123)).toBe(map);
+    expect(map.has(key)).toBe(true);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123 ]));
+    expect(map.size).toBe(1);
+  });
+
+  it('can set multiple values simultaneously.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456, 789 ]))).toBe(map);
+    expect(map.has(key)).toBe(true);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.hasEntry(key, 789)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123, 456, 789 ]));
+    expect(map.size).toBe(3);
+  });
+
+  it('overwrites values when setting them.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect(map.set(key, new Set([ 456, 789 ]))).toBe(map);
+    expect(map.has(key)).toBe(true);
+    expect(map.hasEntry(key, 123)).toBe(false);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.hasEntry(key, 789)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 456, 789 ]));
+    expect(map.size).toBe(2);
+  });
+
+  it('can set entries in the constructor.', async(): Promise<void> => {
+    map = new WrappedSetMultiMap(undefined, [[ key, 123 ], [ key, new Set([ 456, 789 ]) ]]);
+    expect(map.has(key)).toBe(true);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.hasEntry(key, 789)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123, 456, 789 ]));
+    expect(map.size).toBe(3);
+  });
+
+  it('can add a single value.', async(): Promise<void> => {
+    expect(map.set(key, 123)).toBe(map);
+    expect(map.add(key, 456)).toBe(map);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123, 456 ]));
+    expect(map.size).toBe(2);
+  });
+
+  it('can add multiple values.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect(map.add(key, 789)).toBe(map);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.hasEntry(key, 789)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123, 456, 789 ]));
+    expect(map.size).toBe(3);
+  });
+
+  it('can add a a value to a non-existent key.', async(): Promise<void> => {
+    expect(map.add(key, 123)).toBe(map);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123 ]));
+    expect(map.size).toBe(1);
+  });
+
+  it('correctly updates if the new value already exists.', async(): Promise<void> => {
+    expect(map.set(key, 123)).toBe(map);
+    expect(map.add(key, 123)).toBe(map);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123 ]));
+    expect(map.size).toBe(1);
+  });
+
+  it('correctly updates if some new values already exist.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect(map.add(key, new Set([ 456, 789 ]))).toBe(map);
+    expect(map.hasEntry(key, 123)).toBe(true);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.hasEntry(key, 789)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 123, 456, 789 ]));
+    expect(map.size).toBe(3);
+  });
+
+  it('removes the key if it is being set to an empty Set.', async(): Promise<void> => {
+    expect(map.set(key, 123)).toBe(map);
+    expect(map.set(key, new Set())).toBe(map);
+    expect(map.has(key)).toBe(false);
+    expect(map.size).toBe(0);
+  });
+
+  it('can delete a key.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect(map.delete(key)).toBe(true);
+    expect(map.has(key)).toBe(false);
+    expect(map.hasEntry(key, 123)).toBe(false);
+    expect(map.hasEntry(key, 456)).toBe(false);
+    expect(map.get(key)).toBeUndefined();
+    expect(map.delete(key)).toBe(false);
+    expect(map.size).toBe(0);
+  });
+
+  it('can delete a single entry.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect(map.deleteEntry(key, 123)).toBe(true);
+    expect(map.has(key)).toBe(true);
+    expect(map.hasEntry(key, 123)).toBe(false);
+    expect(map.hasEntry(key, 456)).toBe(true);
+    expect(map.get(key)).toEqual(new Set([ 456 ]));
+    expect(map.deleteEntry(key, 123)).toBe(false);
+    expect(map.size).toBe(1);
+  });
+
+  it('removes the key if the last entry is deleted.', async(): Promise<void> => {
+    expect(map.set(key, 123)).toBe(map);
+    expect(map.deleteEntry(key, 123)).toBe(true);
+    expect(map.has(key)).toBe(false);
+    expect(map.hasEntry(key, 123)).toBe(false);
+    expect(map.get(key)).toBeUndefined();
+    expect(map.delete(key)).toBe(false);
+    expect(map.size).toBe(0);
+  });
+
+  it('can clear the entire Map.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    map.clear();
+    expect(map.has(key)).toBe(false);
+    expect(map.size).toBe(0);
+  });
+
+  it('can iterate over the Map.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect([ ...map ]).toEqual([[ key, 123 ], [ key, 456 ]]);
+    expect([ ...map.entries() ]).toEqual([[ key, 123 ], [ key, 456 ]]);
+    expect([ ...map.entrySets() ]).toEqual([[ key, new Set([ 123, 456 ]) ]]);
+    expect([ ...map.keys() ]).toEqual([ key, key ]);
+    expect([ ...map.distinctKeys() ]).toEqual([ key ]);
+    expect([ ...map.values() ]).toEqual([ 123, 456 ]);
+    expect([ ...map.valueSets() ]).toEqual([ new Set([ 123, 456 ]) ]);
+  });
+
+  it('exposes a readonly view on the internal Map for iteration.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    expect([ ...map.asMap() ]).toEqual([[ key, new Set([ 123, 456 ]) ]]);
+  });
+
+  it('supports a forEach call.', async(): Promise<void> => {
+    expect(map.set(key, new Set([ 123, 456 ]))).toBe(map);
+    const result: number[] = [];
+    map.forEach((value): void => {
+      result.push(value);
+    });
+    expect(result).toEqual([ 123, 456 ]);
+  });
+});