System.Xml.Xsl.XsltOld.SortAction.ParseLang C# (CSharp) Method

        private string ParseLang(string value) {
            if(value == null) { // Avt is not constant, or attribute wasn't defined
                return null; 
            }
            if (! XmlComplianceUtil.IsValidLanguageID(value.ToCharArray(), 0, value.Length)) {
                if (this.forwardCompatibility) {
                    return null;
                }
                throw XsltException.Create(Res.Xslt_InvalidAttrValue, Keywords.s_Lang, value);
            }
            return value;
        }