Well, the xib file is the XML file used by the interface constructor.
The header usually contains something similar to this:
<archive type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="7.10">
They then consist of "object" entries that represent the objects contained in nib.
<object class="NSMutableDictionary" key="IBDocument.PluginVersions">
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