.NET (Core and Framework)

<asp:RegularExpressionValidator ID="rwvFilter" runat="server" ControlToValidate="txtFilter"
                                ErrorMessage="Filter is not valid" CssClass="error-message" ValidationExpression="@\\""></asp:RegularExpressionValidator>

Public Class YieldExample
    Implements IEnumerable

    Private _Thing As Double()

    Public Iterator Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
        If IsNothing(Me._Thing) Then
            Throw New InvalidOperationException()
        End If

        For Index As Integer = 0 To Me._Thing.GetUpperBound(0)
            Yield Me._Thing(Index)
        Next
    End Function

End Class

Public Class ExampleEnumerable
    Implements IEnumerable(Of Double)

    Private _Thing As Double()

    Public Function GetEnumerator() As IEnumerator(Of Double) Implements IEnumerable(Of Double).GetEnumerator
        Return New ExampleEnumerator(Me._Thing)
    End Function

    Public Function GetEnumerator1() As IEnumerator Implements IEnumerable.GetEnumerator
        Return Me.GetEnumerator
    End Function
End Class



Public Class ExampleEnumerator
    Implements IEnumerator(Of Double)

    Private _Thing As Double()
    Private _Index As Integer
    Private _curItem As Double

    Public Sub New(ByVal Thing As Double())
        Me._Thing = Thing
        Me._Index = -1
        Me._curItem = Nothing
    End Sub

    Public ReadOnly Property Current As Double Implements IEnumerator(Of Double).Current
        Get
            If IsNothing(Me._curItem) Then
                Throw New InvalidOperationException()
            End If
            Return Me._curItem
        End Get
    End Property

    Public ReadOnly Property Current1 As Object Implements IEnumerator.Current
        Get
            Return Me.Current
        End Get
    End Property

    Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
        'If we are already at the end then return false
        If Me._Index = Me._Thing.GetUpperBound(0) Then
            Return False
        End If
        'Otherwise move to the next position in the array
        Me._Index += 1
        Me._curItem = Me._Thing(Me._Index)
        Return True
    End Function

    Public Sub Reset() Implements IEnumerator.Reset
        Me._Index = -1
        Me._curItem = Nothing
    End Sub

    #Region "IDisposable Support"
 End Class