Regarding Line Number

Public Function GetLineText(ByVal RichTextBox As RichTextBox, _
              ByVal LineNumber As Integer, _
              Optional ByVal FirstLineNumberIsZero _
              As Boolean = False) As String
    If FirstLineNumberIsZero = False Then
      LineNumber = LineNumber - 1
    End If
    If LineNumber < 0 Then Return "Line Does Not Exist" : Exit Function
    If LineNumber > RichTextBox.Lines.Count Then Return "Line Does Not Exist" : Exit Function
    Dim OldCaret As Integer = RichTextBox.SelectionStart
    Dim OldLength As Integer = RichTextBox.SelectionLength
    RichTextBox.HideSelection = False
    Dim Start As Integer = RichTextBox.GetFirstCharIndexFromLine(LineNumber)
    Dim length As Integer = RichTextBox.Lines(LineNumber).Length
    PassStart = Start
    PassLength = length
    RichTextBox.SelectionStart = Start
    RichTextBox.SelectionLength = length
    Dim LineText As String = RichTextBox.SelectedText
    RichTextBox.SelectionStart = OldCaret
    RichTextBox.SelectionLength = OldLength
    Return LineText
End Function