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1:  Public Class RegexTextBox
2:    Inherits TextBox
3:
4:    Private FExpression As String
5:
6:    Public Property Expression() As String
7:    Get
8:      Return FExpression
9:    End Get
10:   Set(ByVal Value As String)
11:     FExpression = Value
12:   End Set
13:   End Property
14:
15:   Protected Overrides Sub OnValidating( _
16:     ByVal e As CancelEventArgs)
17:     If (FExpression = String.Empty OrElse _
18:       Regex.IsMatch(Text, FExpression) OrElse _
19:       AcceptMismatch()) Then
20:       MyBase.OnValidating(e)
21:     Else
22:       e.Cancel = True
23:     End If
24:   End Sub
25:
26:   Private Function AcceptMismatch() As Boolean
27:     Dim Message As String = String.Format( _
28:       "Text {0} does not match expression {1}", _
29:       Text, FExpression)
30:
31:     Return MessageBox.Show(Message, "Validating", _
32:       MessageBoxButtons.OKCancel, MessageBoxIcon.Error) = _
33:       DialogResult.OK
34:   End Function
35:
36: End Class