Keep Some Elements in your _frame In Place
Suppose you want to use the new _frame Layer Naming Convention in your design. You have a main content area and a side bar menu area next to it. But you want the _frame graphic to encompass both the main content AND your menu. If you don't do something special, the _frame will expand with your main content and that menu will move down with the bottom of your _frame! Probably not what you're looking for.
But there is a solution! The trick is to use an _empty container layer for your menu that sticks out of the _frame. It's a technique that takes advantage of the psd2css Online notion of layers that are 'inside' other layers. I wrote about some time ago here:
Here is the PSD file used to make that page: