PowerShell GUI: TextBox Input vorgeben (formatieren)

function GenerateForm {
    Add-Type -A System.Windows.Forms
    # error provider object
    $ep = New-Object System.Windows.Forms.ErrorProvider
    # form object
    $form1 = New-Object System.Windows.Forms.Form -P @{
        ClientSize = '320,80'  
        Text = "Key-Input"  
    }
    # text input 
    $txt = New-Object System.Windows.Forms.TextBox -P @{
        Name = 'txt1'  
        Location = '10,10'  
        Size = '290,20'  
        Anchor = 'Top,Left,Right'  
        MaxLength = 29
        TextAlign = 'Center'  
        Font = New-Object System.Drawing.Font('Microsoft Sans Serif',9)  
        # subscribe KeyDown Event
        add_KeyDown = {
            # handle pasting key via CTRL-V
            if ($_.Control -and $_.KeyCode -eq [System.Windows.Forms.Keys]::V){
                # clear errors
                $ep.Clear()
                $clip = Get-Clipboard -Format Text
                if ($clip -match '(([2-46-9a-df-hj-km-np-rt-y]){5}-){4}([2-46-9a-df-hj-km-np-rt-y]){5}'){  
                    $txt.Text = $matches
                }
                $txt.SelectionStart = $txt.Text.Length
            }
        }
        # subscribe KeyPress event
        add_KeyPress = {
            # clear errors
            $ep.Clear()
            # please note letters E, U, L, A, O, S, I, Z, AND numbers 1, 0, 5 are never used in the product key combination.
            if ($_.KeyChar -match '[2-46-9a-df-hj-km-np-rt-y]'){  
                $_.Handled = $false
                # convert to upper case
                $_.KeyChar = $_.KeyChar.toString().toUpper()
                # add dash after every five characters
                if ($txt.Text.Length -in (5,11,17,23)){
                    $txt.Text += "-"  
                    $txt.SelectionStart = $txt.Text.Length
                }
            # handle backspace key
            }elseif($_.KeyChar -eq [System.Windows.Forms.Keys]::Back){
                $_.Handled = $false
                # jump over dash on backspace
                if ($txt.Text.EndsWith('-')){  
                    $txt.Text = $txt.Text.Substring(0,$txt.Text.Length-1)
                    $txt.SelectionStart = $txt.Text.Length
                }
            # invalid char entered ignore input
            }else{
                $_.Handled = $true
            }
        }

        add_Click = {
            $txt.SelectionStart = $txt.Text.Length
        }
        add_DoubleClick = {
            $txt.SelectionStart = $txt.Text.Length
        }
    }
    # add button
    $btn = New-Object System.Windows.Forms.Button -P @{
        Text = "OK"  
        Location = '10,40'  
        Size = '300,30'  
        Anchor = 'Bottom,Left,Right'  
        add_Click = {
            # check general format of key
            if ($txt.Text -match '^(([2-46-9a-df-hj-km-np-rt-y]){5}-){4}([2-46-9a-df-hj-km-np-rt-y]){5}$'){  
                $form1.Close()
            }else{
                $ep.SetError($txt,'The key should be in this format XXXXX-XXXXX-XXXXX-XXXXX-XXXXX !')  
            }
        }
    }
    $form1.Controls.AddRange(@($txt,$btn))
    [void]$form1.ShowDialog()
    $txt.Text
}
GenerateForm

function GenerateForm {
    Add-Type -A System.Windows.Forms
    # error provider object
    $ep = New-Object System.Windows.Forms.ErrorProvider
    # form object
    $form1 = New-Object System.Windows.Forms.Form -P @{
        ClientSize = '320,80'  
        Text = "Key-Input"  
    }
    # text input with masked textbox
    $txt = New-Object System.Windows.Forms.MaskedTextBox -P @{
        Name = 'txt1'  
        Location = '10,10'  
        Size = '290,20'  
        Anchor = 'Top,Left,Right'  
        AsciiOnly = $true
        # set mask: set to uppercase and onyl use ASCII Letters and Numbers with dashes
        Mask = '>AAAAA-AAAAA-AAAAA-AAAAA-AAAAA'  
        Font = New-Object System.Drawing.Font('Microsoft Sans Serif',9)  

        add_TextChanged ={
            $ep.Clear()
        }
    }
    # add button
    $btn = New-Object System.Windows.Forms.Button -P @{
        Text = "OK"  
        Location = '10,40'  
        Size = '300,30'  
        Anchor = 'Bottom,Left,Right'  
        add_Click = {
            # check if mask is completed
            if (!$txt.MaskFull){
                $ep.SetError($txt,'The key is not complete!')  
                return
            }
            # check general format of key
            if ($txt.Text -match '^(([2-46-9a-df-hj-km-np-rt-y]){5}-){4}([2-46-9a-df-hj-km-np-rt-y]){5}$'){  
                $form1.Close()
            }else{
                $ep.SetError($txt,'The key should be in this format: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX (letters E, U, L, A, O, S, I, Z, AND numbers 1, 0, 5 should never be used) !')  
            }
        }
    }
    $form1.Controls.AddRange(@($txt,$btn))
    [void]$form1.ShowDialog()
    $txt.Text
}
GenerateForm