In many ways, we are already familiar with a classical version of it. Doppler shifting... when sound waves (like from a fast moving car), changes in pitch (wavelength/frequency) due to lengthening of the distance between emitted wave peaks. For light (EM waves), there is an element of this Doppler shifting if things are moving fast towards (blue) or away from us (red).

Thanks for expanding, I'm not familiar with that technology very much so it's still a bit fuzzy for me, but I think I get it in a sort of general sense!

Technically, the problem with that question is more to do with our limited experience of reality and the Universe. We have to use analogies to get our heads around the concepts... .which neccessarily means that we assume that we have to expand INTO something... because that is the way we normally perceive expansion. However, for this, the expansion is of the Space-Time metric, which isn't quite the same thing as the expansion that we experience with everyday objects! It is more akin to your ruler which you measure things with expanding (changing size between the centimetre pips)?

Interesting explanation yet regardless of whether things are expanding within a set limit or more than that it still begs the question, what's outside of that? And I've seen a good amount of theories put out there yet I just don't think anyone alive probably knows for sure since it's beyond our ability to observe. We may never be able to know? It really does make one wonder though! Like.. Is there just an infinite amount of empty space outside the perceivable universe? Or..?? Lol. Fun to think about whatever the case.

It is more that there currently is no need to postulate a "thing" to expand into! So, it is more of the Occam's Razer solution at the moment...

Perhaps though there's no need to theorize about many things, yet we still do and I think a lot of richness in life comes from that. :)