One new feature in Flash Builder 4.5 that’s small but incredibly useful is the new block selection mode. (Sometimes known as multi-line selection mode.)
This feature allows you to edit the same position in a block of lines at once. This is very useful when you’re copying and pasting a block of code and you only need to change one thing, like a variable name, in several lines of code. The video below demonstrates this much more clearly than I could explain it in text.
To toggle block selection mode, click this toolbar button (it’s close to the “Mark Occurrences” highlighter button):
You can also use the keyboard shortcut Ctrl/Cmd+Alt+A.
As promised, here’s a video demo I put together showing a couple of my most common uses for Block Selection mode. (You’ll obviously want to watch it in full screen, or at least at a larger size on the video’s Vimeo page.)