Unsolved TextField Validation in QML

[pra7]

I am having a TextField which allows the user to enter time and I have used RegValidator to validate. Currently, i need to fill with "0" when user clicks on backspace. Following is the code:

TextField {
    id:textField
    text:"11:11:11"
    width:200
    height:80
    font.pointSize: 15
    color:"white"
    inputMask: "99:99:99"
    validator: RegExpValidator { regExp: /^([0-1\s]?[0-9\s]|2[0-3\s]):([0-5\s][0-9\s]):([0-5\s][0-9\s])$ / }
    horizontalAlignment: Text.AlignHCenter
    verticalAlignment: Text.AlignVCenter
    inputMethodHints: Qt.ImhDigitsOnly
}