function _createUnattachedMasterEditor(doc) {
        // attach to the hidden containers DOM node if necessary
        if (!_$hiddenEditorsContainer) {
            _$hiddenEditorsContainer = $("#hidden-editors");
        }
        // Create an editor
        var editor = _createEditorForDocument(doc, true, _$hiddenEditorsContainer);
        // and hide it
        editor.setVisible(false);
    }
Creates a hidden, unattached master editor that is needed when a document is created for the
sole purpose of creating an inline editor so operations that require a master editor can be performed
Only called from Document._ensureMasterEditor()
The editor view is placed in a hidden part of the DOM but can later be moved to a visible pane
when the document is opened using pane.addView()
@param {!Document} doc - document to create a hidden editor for