Why isn’t the CSS property ‘line-height’ letting me make tight line-spaces in Chrome?

I’ve noticed in both Firefox and Chrome that if you set the HTML5 doctype there’s a minimum line-height for inline elements. For block elements you can set the line-height to whatever you want, even make the lines overlap.

If you don’t set the HTML5 doctype, there’s no minimum line-height for either block or inline elements.