System.Xml.Xsl.XsltOld.InputScopeManager.ResolveXPathNamespace C# (CSharp) Method

        public string ResolveXPathNamespace(string prefix) {
            Debug.Assert(prefix != null);
            if (prefix.Length == 0) {
                return string.Empty;
            }
            return ResolveNonEmptyPrefix(prefix);
        }

        private PrefixQName       qname; // When we not have AVTs at all we can do this. null otherwise.

        private static PrefixQName CreateAttributeQName(string name, string nsUri, InputScopeManager manager) {
            // if name == "xmlns" we don't need to generate this attribute.
            // to avoid i'ts generation we can return false and not add AtributeCation to it's parent container action
            // for now not creating this.qname will do the trick at execution time
            if (name  == "xmlns") return null;
            if (nsUri == XmlReservedNs.NsXmlNs) {
                throw XsltException.Create(Res.Xslt_ReservedNS, nsUri);
            }

            PrefixQName qname = new PrefixQName();
            qname.SetQName(name);

            qname.Namespace = nsUri != null ? nsUri : manager.ResolveXPathNamespace(qname.Prefix);

            if (qname.Prefix.StartsWith("xml", StringComparison.Ordinal)) {
                if (qname.Prefix.Length == 3) { // prefix == "xml"
                    if (qname.Namespace == XmlReservedNs.NsXml && (qname.Name == "lang" || qname.Name == "space")) {
                        // preserve prefix for xml:lang and xml:space
                    }
                    else {
                        qname.ClearPrefix();
                    }
                }
                else if (qname.Prefix == "xmlns") {
                    if (qname.Namespace == XmlReservedNs.NsXmlNs) {
                        // if NS wasn't specified we have to use prefix to find it and this is imposible for 'xmlns' 
                        throw XsltException.Create(Res.Xslt_InvalidPrefix, qname.Prefix);
                    }
                    else {
                        qname.ClearPrefix();
                    }
                }
            }
            return qname;
        }