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

        private string ResolveNonEmptyPrefix(string prefix) {
            Debug.Assert(this.scopeStack != null, "PushScope wasn't called");
            Debug.Assert(prefix != null || prefix.Length != 0);
            if (prefix == Keywords.s_Xml) {
                return Keywords.s_XmlNamespace;
            }
            else if (prefix == Keywords.s_Xmlns) {
                return Keywords.s_XmlnsNamespace;
            }

            for (InputScope inputScope = this.scopeStack; inputScope != null; inputScope = inputScope.Parent) {
                string nspace = inputScope.ResolveNonAtom(prefix);
                if (nspace != null) {
                    return nspace;
                }
            }
            throw XsltException.Create(Res.Xslt_InvalidPrefix, prefix);
        }