function containsKey(keys, key) {
		if (Array.isArray(keys)) {
			return keys.indexOf(key) !== -1;
		} else {
			return keys === key;
		}
	}
Checks if the pressed key is any of the configured modifier keys for
a specified behavior.

@param {number | number[]} keys 
@param {number} key 

@returns {boolean} `true` if `keys` contains or equals `key`