The sage terminal returns the following, but the notebook interface omits the "Base Class", "String Form", "Namespace", and "Length":
sage: NaN?
Type: Expression
Base Class: type 'sage.symbolic.expression.Expression'
String Form: NaN
Namespace: Interactive
Length: 0
File: /SAGE_DIR/local/lib/python2.6/site-packages/sage/categories/commutative_rings.py
Definition: NaN(self, *args, **kwds)
Docstring:
x.__init__(...) initializes x; see x.__class__.__doc__ for signature
