Not just with a mouse. The frames can be detected automatically. Imagine a typical IDE where:

  while (...) {

Automatically inserted the next `}` and moved the cursor between it. But in the frame based editor, the `{` and `}` are elided from the presentation, replaced with a colored block or frame around the inner kernel of the while loop.

  +++ while (condition)
  +   --- if (condition)
  +   -   *** actions
  +   ------------------
  ++++++++++++++++++++++

Scratch (the example in Figure 1) is definitely a mouse driven interface, but beyond that and its visual presentation, it's more a cousin to the frame based model than a precise representation.

It gives you a better (arguable?), structural way to view code, and to edit it with both text input and mouse.