Post with Amazon Kindle block producing validation error

[itowhid06]

Bug Description

In the WordPress Block Editor, if the Amazon Kindle block is added then a validation error occurs.

As there is a type="text/html" attribute-value combination present in the iframe generated from the Amazon Kindle embed and type is not a standard <iframe> attribute, that is why the validation error occurs. Though type is a non-standard attribute, it is fairly common in some embeds.

Expected Behaviour

Embeds with fairly common non-standard attributes like type should not produce validation errors.

Steps to reproduce

1. Create a post with Amazon Kindle block.
2. Validate the post.
3. See the validation error in back-end.

Screenshots

Validation error with Amazon Kindle block

Additional context

• WordPress version:
• Plugin version:
• Gutenberg plugin version (if applicable):
• AMP plugin template mode:
• PHP version:
• OS:
• Browser: [e.g. chrome, safari]
• Device: [e.g. iPhone6]

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