On Mon, 28 Feb 12:06 (-0300), Ben Jackson wrote:

I was selecting text using the shift/option/arrow keys today and at some point my selection turned rectangular! However to my dismay I'm unable to figure out what I did that allowed me to switch over. What's the secret?

You can select Text with Shift pressed and if you then press Alt/Option you get in Column Mode, I am not sure if this answers your Question.