Returns a string representing the content of the element, this should typically be;
            WordElement.Content => theWord
            NotWordElement.Content => -theWord
            GroupElement.Content => null
            PhraseElement.Content => thePhrase (no quotes)
            
| C# | Visual Basic | Visual C++ | 
public override string Content { get; }
Public Overrides ReadOnly Property Content As String
public: virtual property String^ Content { String^ get () override; }