public string GetTextBody (TextFormat format)
{
var multipart = Body as Multipart;
if (multipart != null) {
string text;
if (TryGetMultipartBody (multipart, format, out text))
return text;
} else {
var body = Body as TextPart;
if (body != null && body.IsFormat (format))
return body.Text;
}
return null;
}