What, you don't intuitively call that line a "horizontal rule"? That's what hr in <hr> is for.

For general reference, you can always highlight a chunk of page, right-click, and choose view selection source, and see the html behind just thatlittle bit of page, in Firefox. I dunno how to do this on a Mac, though of course you can always also select view and page source up top; then it just takes longer to find the section you had in mind.

:D