Page 141 of RB 2012.5 Manual says to highlight a section you "Click and hold the left mouse button at the upper right corner of the rectangular section..." Shouldn't this say the upper left corner?
In Editable Notation Mode, when I click and hold the left mouse button with the intent of highlighting a group of notes, the cursor jumps to the left edge of the window. It won't allow me to draw a rectangle.
How do I make this work?

Make sure you are in edit mode. At the top of windows from left to right, you should see a button for "Opt", then "Print", then three icons. The first icon is just plain notation mode for viewing; second icon shows normal notes for editing; the third icon shows editable notes with velocity (vertical blue lines) and length (horizontal blue lines). Make sure you click on the 2nd or 3rd icon. From there, you should be able to highlight several notes by drawing a box either from the top right (to lower left) or as you indicated from top left (to lower right).

Hope that helps.

Yes, it should say upper Left corner (if you want to drag down and to the right)

You could also start in upper Right and drag down and to the left, but either way you can drag and highlight the section.
And it seems to work here, just tested.

To test I highlighted a section in Editable Notation, transposed it and it reflected the change..

Thanks. Got it working now.