This select modifies the left Expando's easing function. An Expando can have an easeIn and an easeOut parameter. This sets both.
Some easing functions break when used with width: (negative width? but how?). Be warned.
This is a BorderContainer (the window). Each of the panes is set to one of "left", "right", or "center". The left and right panes are ExpandoPanes (they collapse).
What does a FloatingPane look like here?