Instances of the NSNib class serve as object wrappers, or containers, for Interface Builder nib files. An NSNib object keeps the contents of a nib file resident in memory, ready for unarchiving and instantiation.
Only available in 10.3 and up.
Unlike what you could hope, the NSNib object does not provide any way of inspecting the hierarchy of the .nib file; it only provides initialization methods that load the nib from disk and instantiation methods that unarchive and initialize the objects in the .nib. You may pipe the output of the /usr/bin/nibtool program to inspect a nib without instantiating it.
Use NSNib when [NSBundle loadNibNamed:owner:] doesn’t work, like for the rare CLI app that needs to load a nib. ;)