Position: option 'of' accepts jQuery object unless it wraps document

One of the undocumented accepted types ( see #5962 - Position: option 'of' can be other than type selector, undocumented ) of the position option 'of' is a jQuery object.

The 'of' option as of 1.8.4 accepts a selector string directly:

  of: "#parent",

or you can wrap the selector in a jQuery object before passing to 'of':

  of: $("#parent"),

Another accepted value of 'of' is the document

  of: document,

but if you wrap the document in a jQuery object like so:

  of: $(document),

it fails. This seems a bit inconsistent.