System.Xml.Schema.DtdValidator.ValidateStartElement C# (CSharp) Method

        private void ValidateStartElement() {
            if (context.ElementDecl != null) {
                Reader.SchemaTypeObject =  context.ElementDecl.SchemaType;

                if (Reader.IsEmptyElement  && context.ElementDecl.DefaultValueTyped != null) {
                   Reader.TypedValueObject = context.ElementDecl.DefaultValueTyped;
                   context.IsNill = true; // reusing IsNill - what is this flag later used for??
                }
                if ( context.ElementDecl.HasRequiredAttribute ) {
                    attPresence.Clear();
                }
            }
            
            if (Reader.MoveToFirstAttribute()) {
                do {
                    try {
                        reader.SchemaTypeObject = null;
                        SchemaAttDef attnDef = context.ElementDecl.GetAttDef( new XmlQualifiedName( reader.LocalName, reader.Prefix) );
                        if (attnDef != null) {
                            if (context.ElementDecl != null && context.ElementDecl.HasRequiredAttribute) {
                                attPresence.Add(attnDef.Name, attnDef);
                            }
                            Reader.SchemaTypeObject = attnDef.SchemaType;
                            
                            if (attnDef.Datatype != null && !reader.IsDefault) { //Since XmlTextReader adds default attributes, do not check again
                                // set typed value
                                CheckValue(Reader.Value, attnDef);
                            }
                        }
                        else {
                            SendValidationEvent(Res.Sch_UndeclaredAttribute, reader.Name);
                        }
                    }
                    catch (XmlSchemaException e) {
                        e.SetSource(Reader.BaseURI, PositionInfo.LineNumber, PositionInfo.LinePosition);
                        SendValidationEvent(e);
                    }
                } while(Reader.MoveToNextAttribute());
                Reader.MoveToElement();
            }
            
        }