' Retrieve the next formatted text run for the text source.
Public Overrides Function GetTextRun(ByVal textSourceCharacterIndex As Integer) As TextRun
    ' Determine whether the text source index is in bounds.
    If textSourceCharacterIndex < 0 Then
        Throw New ArgumentOutOfRangeException("textSourceCharacterIndex", "Value must be greater than 0.")
    End If

    ' Determine whether the text source index has exceeded or equaled the text source length.
    If textSourceCharacterIndex >= _text.Length Then
        ' Return an end-of-paragraph indicator -- a TextEndOfParagraph object is a special type of text run.
        Return New TextEndOfParagraph(1)
    End If

    ' Create and return a TextCharacters object, which is formatted according to
    ' the current layout and rendering properties.
    If textSourceCharacterIndex < _text.Length Then
        ' The TextCharacters object is a special type of text run that contains formatted text.
        Return New TextCharacters(_text, textSourceCharacterIndex, _text.Length - textSourceCharacterIndex, New CustomTextRunProperties()) ' The layout and rendering properties -  The text store length -  The text store index -  The text store
    End If

    ' Return an end-of-paragraph indicator if there is no more text source.
    Return New TextEndOfParagraph(1)
End Function