/// <summary>
/// Return a location of the given JSON token `t` in the document `j`.
/// </summary>
/// <param name="jsonDoc"></param>
/// <param name="jsonToken"></param>
/// <returns>a string in this format `fileName:lineNumber:linePosition`</returns>
private static string Location(IJsonDocument jsonDoc, JToken jsonToken)
{
// up cast.
IJsonLineInfo x = jsonToken;
return(x == null ?
null :
$"{ObjectPath.FileNameNorm(jsonDoc.FileName)}:{x.LineNumber}:{x.LinePosition}");
}
