ilyanengen

// Create CustomView.xib, set File's Owner to CustomView. 
// Link the top level view in the XIB to the contentView outlet.

class CustomView : UIView {
    @IBOutlet private var contentView:UIView?
    // other outlets
    
    override init(frame: CGRect) { // for using CustomView in code
        super.init(frame: frame)
        self.commonInit()

ilyanengen

import UIKit

/// A validation rule for text input.
public enum TextValidationRule {
    /// Any input is valid, including an empty string.
    case noRestriction
    /// The input must not be empty.
    case nonEmpty
    /// The enitre input must match a regular expression. A matching substring is not enough.
    case regularExpression(NSRegularExpression)