When a user pastes data into my frontend forms wysiwyg field, very often it comes along with many divs, iframes, inline styles and classes. The big problem with this is that it ruins the styling of the website.
The field wysiwyg use the WP function wp_kses_post() to sanitize the input value. You can create your own function callback to sanitize the user input. Please read more on the documentation https://docs.metabox.io/sanitization/
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