I have always tended to assume that any of my more philosophical questions about mathematics would off-topic for Math.SE. As such, I have tended to restrict (or try to restrict) my questions to those of a more purely technical nature. However, when posting my most recent question I realized that there is a philosophy tag whose tag-wiki suggests that, in fact, philosophy of mathematics questions are on-topic for Math.SE.
Given that Philosophy.SE is a fairly small community (at least in terms of active members) and that the active members who can respond to somewhat mathematically sophisticated questions are even fewer, this was encouraging to find. It seems that some of these questions would receive much more attention, and mathematically informed answers, on this SE.
Which brings me to my question. What sort of questions within the philosophy of mathematics would be on-topic for this SE?