With <x id="START_TAG_STRONG" ctype="x-strong" equiv-text="<strong>"/>Hide<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/> or <x id="START_TAG_STRONG" ctype="x-strong" equiv-text="<strong>"/>Blur thumbnails<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/>, a confirmation will be requested to watch the video.
The username is a unique identifier of your account on this and all the other instances. It's as unique as an email address, which makes it easy for other people to interact with it.