Coverage. Without 'width' and 'height' attributes

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@[example](video-123)
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<div class="block-embed block-embed-service-example"><iframe type="text/html" src="https://example.com/embed/video-123/42" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe></div>
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@[example](x)
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<div class="block-embed block-embed-service-example"><iframe type="text/html" src="https://example.com/embed/x/42" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe></div>
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