HTML : PHP code inside a Javascript's "document.write()"

Описание: HTML : PHP code inside a Javascript's "document.write()"
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As promised, I have a hidden feature that I want to share with you.
This is a YouTube's feature which works on Desktop.
First, Make sure this video is playing.
Then, type the letters 'awesome' on the keyboard.
You will see a flashing rainbow instead of a regular progress bar on YouTube.

A brief presentation of myself,
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HTML : PHP code inside a Javascript's "document.write()"
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a HTML PHP Javascript's "document.write()" : code inside