void OnDocumentLineCountChanged()
{
int documentLineCount = Document != null ? Document.LineCount : 1;
int newLength = documentLineCount.ToString(CultureInfo.CurrentCulture).Length;
// The margin looks too small when there is only one digit, so always reserve space for
// at least two digits
if (newLength < 2)
newLength = 2;
if (newLength != maxLineNumberLength) {
maxLineNumberLength = newLength;
InvalidateMeasure();
}
}