Templates Name question

[doane]

While working on some new websites I noticed several of the templates I was looking at have the name "PageControl:topleft" applied to the upper bar, the upper image headier, the menu bar and the upper site name. What is this name for? It's not used for a link to the top of the page.

Here's another example, the "Vista" template has the name on the logo at the top left and on the menu bar.