material-components_material-components-ios/components/FlexibleHeader/docs/subclassing-considerations.md

Subclassing considerations

A subclass of your view controller may add additional views in their viewDidLoad, potentially resulting in the header being covered by the new views. It is the responsibility of the subclass to take the z-index into account:

Swift

view.insertSubview(myCustomView, belowSubview: headerViewController.headerView)

Objective-C

[self.view insertSubview:myCustomView belowSubview:self.headerViewController.headerView];