Wave your mouse over the diagram and the border of the section you're hovering over will turn red. Click and the actual page element will be highlighted in green. If the element has a border, it will turn red. (Firefox and Internet Explorer tested.)
If a particular section does not blink, it's probably because it's hidden by a section in front of it. If that is a case, try enabling "Indicate Border" by clicking the checkbox, although note that the way it shifts the screen can be disorienting.
Finally, because this text may make it hard to view both the diagram and the real objects (in cases like the header), you can hide this text by clicking "Toggle Text" on the top right.
| Switch Skins: | Indicate Border |