Old proxy lists sorted proxies into three levels. A transparent proxy passes your real address along in a header. An anonymous one removes your address but adds headers that admit a proxy is in the way. An elite, or high-anonymity, proxy adds nothing.
The levels matter little today. For https sites the proxy only carries an encrypted tunnel and cannot add headers to the request at all. What a site judges now is the address itself: its network, its history and whether the browser behind it looks real.
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