private VirtualTreePoint GetStartPoint(SourceText text, AttributeSyntax node, EnvDTE.vsCMPart part)
            {
                int startPosition;

                switch (part)
                {
                    case EnvDTE.vsCMPart.vsCMPartName:
                    case EnvDTE.vsCMPart.vsCMPartAttributes:
                    case EnvDTE.vsCMPart.vsCMPartHeader:
                    case EnvDTE.vsCMPart.vsCMPartWhole:
                    case EnvDTE.vsCMPart.vsCMPartBodyWithDelimiter:
                    case EnvDTE.vsCMPart.vsCMPartHeaderWithAttributes:
                        throw Exceptions.ThrowENotImpl();

                    case EnvDTE.vsCMPart.vsCMPartAttributesWithDelimiter:
                    case EnvDTE.vsCMPart.vsCMPartBody:
                        throw Exceptions.ThrowEFail();

                    case EnvDTE.vsCMPart.vsCMPartWholeWithAttributes:
                        startPosition = node.GetFirstToken().SpanStart;
                        break;

                    case EnvDTE.vsCMPart.vsCMPartNavigate:
                        startPosition = node.Name.SpanStart;
                        break;

                    default:
                        throw Exceptions.ThrowEInvalidArg();
                }

                return new VirtualTreePoint(node.SyntaxTree, text, startPosition);
            }