XIB

As of MacOS 10.3 Apple moved away from the binary encoded nib files, and towards the xml encoded XIB files, for their interface definitions

The xib file format is actually quite easy to understand, it is the responsability of the object encodeing and decoding, it to insure that it's attributes are read correctly.

Here is a commented example of a XIB file. For easy reading open it in a syntax highliting editor using XML highlighting.