Process array, object, or string as a string of classes delimited by a space.

If val is an array, all members of it and its subarrays are counted as classes. If escaping is an array, then whether or not the item in val is escaped depends on the corresponding item in escaping. If escaping is not an array, no escaping is done.

If val is an object, all the keys whose value is truthy are counted as classes. No escaping is done.

If val is a string, it is counted as a class. No escaping is done.