System.Xml.Xsl.Xslt.XsltLoader.XslAnalyzeString C# (CSharp) Method

        private XslNode XslAnalyzeString() {
            ContextInfo ctxInfo = input.GetAttributes(analyzeStringAttributes);

            string select = ParseStringAttribute(0, "select");
            string regex  = ParseStringAttribute(1, "regex" );
            string flags  = ParseStringAttribute(2, "flags" );
            if (flags == null) {
                flags = "";
            }

            ReportNYI("xsl:analyze-string");

            XslNode matching = null;
            XslNode nonMatching = null;
            QName parentName = input.ElementName;
            if (input.MoveToFirstChild()) {
                do {
                    switch (input.NodeType) {
                    case XmlNodeType.Element:
                        if (input.IsXsltKeyword(atoms.MatchingSubstring)) {
                            ContextInfo ctxInfoChld = input.GetAttributes();
                            CheckError(nonMatching != null, /*[???]*/SR.Xslt_AnalyzeStringChildOrder);
                            CheckError(matching    != null, /*[???]*/SR.Xslt_AnalyzeStringDupChild, atoms.MatchingSubstring);
                            // The current template rule becomes null, so we must not allow xsl:apply-import's within this element
                            input.CanHaveApplyImports = false;
                            matching = SetInfo(f.List(), LoadInstructions(), ctxInfoChld);
                        } else if (input.IsXsltKeyword(atoms.NonMatchingSubstring)) {
                            ContextInfo ctxInfoChld = input.GetAttributes();
                            CheckError(nonMatching != null, /*[???]*/SR.Xslt_AnalyzeStringDupChild, atoms.NonMatchingSubstring);
                            input.CanHaveApplyImports = false;
                            nonMatching = SetInfo(f.List(), LoadInstructions(), ctxInfoChld);
                        } else if (input.IsXsltKeyword(atoms.Fallback)) {
                            XslFallback();
                        } else {
                            ReportError(/*[XT_017]*/SR.Xslt_UnexpectedElement, input.QualifiedName, parentName);
                            input.SkipNode();
                        }
                        break;
                    case XmlNodeType.Whitespace:
                    case XmlNodeType.SignificantWhitespace:
                        break;
                    default:
                        Debug.Assert(input.NodeType == XmlNodeType.Text);
                        ReportError(/*[XT_017]*/SR.Xslt_TextNodesNotAllowed, parentName);
                        break;
                    }
                } while (input.MoveToNextSibling());
            }
            CheckError(matching == nonMatching, /*[XTSE1130]*/SR.Xslt_AnalyzeStringEmpty);

            ctxInfo.SaveExtendedLineInfo(input);

            return null;
        }