Visually debugging XSL-FO stylesheets

When developing XSL-FO stylesheets sooner or later you will see something that doesn’t look as intended: It has the wrong margin, padding, line height, floats in the wrong place, etc. If you have no visual debugging tool, the quickest way to check for errors is setting a border or background attribute on the element in question. <curmudgeon>Just like we debugged web layouts in 1999! We had nothing like that fancy Firebug plugin, just our trusty notepad and bare HTML!