def bind(object):
    """Return a copy of this field which is bound to context.

        The copy of the Field will have the 'context' attribute set
        to 'object'.  This way a Field can implement more complex
        checks involving the object's location/environment.

        Many fields don't need to be bound. Only fields that condition
        validation or properties on an object containing the field
        need to be bound.
        """
