What's the code equivalent to the autoresizing mask anchoring options in IB?

Answer 1

Anything you can do in Interface Builder you can do through code.

[myTextField setAutoresizingMask:(NSViewMaxXMargin | NSViewMinYMargin)];

This means that the margin between the right edge of the textView and its superview will be flexible, as will the margin between the bottom edge and its superview. Everything else is static.