WWYD Wedensday: More of some questions for you all

So, I know a few things about finances and learn even more as I go along.

This is a question I thought of yesterday and today even more so. I plan on looking it up online as well but here goes it:

When talking about housing expenses and the percentage it should take of your income I've heard 25% and 35% of your income should be allocated towards housing.

What exactly is included in those numbers? Is that just rent or mortgage or is it all living expenses like rent/mortgage, electricity, insurance (rental or house), gas etc...

Also is that a percentage of gross or net income?

What happens when your percentage of income is not enough to live on in the areas you have to choose from to live? Is this still a big no-no?

So this week is more of a what do you know than it is a WWYD question. I hope that is okay for my readers but I really had this question looming and it made it difficult for me to come up with anything else.

I suppose I could pose it as a WWYD, as in WWYD if your percentage of income was lower than what your housing costs were. Yes, we'll do that in here as well.

So WWYD? and WDYK (What do you know)?