Everyone has used the F16 find function, but perhaps not to its fullest extent.
Key in H ' ' A, hit enter. Every line in the source is now hidden -- assuming it has even a single space.
Now key in F EXSR A, hit enter again. Next F BEGSR A, then F ENDSR A...
There's a quick snapshot of what's branching where and from within what.
In Edit mode, you'll have a separator line with the number of how many lines in between are hidden. In browse, there will be no separator.
For the edit mode, you can then key in SFxx (show first) or SLxx (show last) in the sequence area of the separator line to see xx number of lines that are currently hidden.