The source linked debugger also provides a set of buttons to allow you to view ancestor invocation frames.
-+--------+----------+----------+
|Frame Up|Frame Down|Frame Back|
-+--------+----------+----------+
The Frame Up button will show you the invocation before the one you are viewing. That means that the arrow will point to the place the invocation you are currently viewing was called from. Repeatedly hitting the Frame Up button will cause you to continue to traverse up through parent invocations, eventually stopping at the goal you typed at the top level prompt.
The Frame Down button may be used after you have framed up to take you back down toward the current invocation frame.
The Frame Back button will immediately take you back to the current invocation frame. This may also be used when you have framed up or scrolled the source window, and want to instantly scroll back to show the current invocation frame, or even if you are viewing another source file in the source window and want to get back.
In order to remind you when the goal you are viewing is not the current invocation frame, the arrow shown in the source window is hollow, or "ghosted", rather than the usual solid arrow.
|\
+-------+ \
| >
+-------+ /
|/
When you have framed up, certain travel buttons are interpreted relative to the frame you are currently viewing. Skip will skip over the invocation you are viewing (this is very handy if you have accidentally crept into a procedure you don't want to debug). Redo and Fail will take you to the call and fail ports of the selected invocation, respectively. All other travel buttons are disabled when you have framed up. You must either frame down or frame back in order to travel from the current invocation.