AbstractClass-class     Reference Class representing a non instantiable
                        class
Content-class           An abstract reference class representing
                        content that can belong to an Element
Document-class          Reference Class representing an XML document
DomBuilder-class        Create a xmlr object tree based on parsing
                        events
Element-class           Element, A reference class representing an XML
                        tag
Parser-class            Parse an xml string and create sax like events
Stack-class             A general purpose linked stack
Text-class              Reference class representing text content
isRc                    Common utility functions
xmlImporter             XML import functions
xmlr                    xmlr
xmlrToDataFrame         Create a data frame from a xmlr Element
