PropertyBag
A PropertyBag represents a collection of name value pairs
            that allows duplicate entries with the same key. Methods
            are provided for adding a new pair as well as for setting
            a key to a single value. All keys are strings but values
            may be of any type. Null values are not permitted, since
            a null entry represents the absence of the key.
            
                
Gets or sets the list of values for a particular key
            
Gets a collection containing all the keys in the property set
            
public PropertyBag()
Adds a key/value pair to the property set
            
Returns an XmlNode representing the PropertyBag after
            adding it as a child of the supplied parent node.
            
Gets a flag indicating whether the specified key has
            any entries in the property set.
            
Gets a single value for a key, using the first
            one if multiple values are present and returning
            null if the value is not found.
            
Sets the value for a key, removing any other
            values that are already in the property set.
            
Returns an XmlNode representing the current PropertyBag.
            
Tries to retrieve list of values.