Stripe: This Element will be mounted to a DOM element that contains child nodes

I'm running stripe v3 and it's giving me this warning in the web console.

This Element will be mounted to a DOM element that contains child nodes.

1. Why does it matter if the element contains "child nodes".
2. How should this best be resovled to remove the warning and resolve the issue.

My Stripe code is currently the same code recommended in the setup of Stripe Elements.

Ref: https://stripe.com/docs/stripe-js/elements/quickstart

// Create a Stripe client
var stripe = Stripe('pk_test_bJA9VLD3BN4LYxPWPfJ5vcjk');

// Create an instance of Elements
var elements = stripe.elements();

// Custom styling can be passed to options when creating an Element.
// (Note that this demo uses a wider set of styles than the guide below.)
var style = {
  base: {
    color: '#32325d',
    lineHeight: '18px',
    fontFamily: '"Helvetica Neue", Helvetica, sans-serif',
    fontSmoothing: 'antialiased',
    fontSize: '16px',
    '::placeholder': {
      color: '#aab7c4'
    }
  },
  invalid: {
    color: '#fa755a',
    iconColor: '#fa755a'
  }
};

// Create an instance of the card Element
var card = elements.create('card', {style: style});

// Add an instance of the card Element into the `card-element` <div>
card.mount('#card-element');

// Handle real-time validation errors from the card Element.
card.addEventListener('change', function(event) {
  var displayError = document.getElementById('card-errors');
  if (event.error) {
    displayError.textContent = event.error.message;
  } else {
    displayError.textContent = '';
  }
});

// Handle form submission
var form = document.getElementById('payment-form');
form.addEventListener('submit', function(event) {
  event.preventDefault();

  stripe.createToken(card).then(function(result) {
    if (result.error) {
      // Inform the user if there was an error
      var errorElement = document.getElementById('card-errors');
      errorElement.textContent = result.error.message;
    } else {
      // Send the token to your server
      stripeTokenHandler(result.token);
    }
  });
});