private TriState ParseYesNoAttribute(int attNum, string attName)
{
Debug.Assert(!_input.IsRequiredAttribute(attNum), "All Yes/No attributes are optional.");
if (_input.MoveToXsltAttribute(attNum, attName))
{
switch (_input.Value)
{
case "yes": return TriState.True;
case "no": return TriState.False;
default:
if (!_input.ForwardCompatibility)
{
ReportError(/*[XT_028]*/SR.Xslt_BistateAttribute, attName, "yes", "no");
}
break;
}
}
return TriState.Unknown;
}