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Save-Data

The Save-Data header field is a boolean which, in requests, indicates the client's preference for reduced data usage. For example you coudl serve a much lighter version of a website.

$saveData = (isset($_SERVER["HTTP_SAVE_DATA"]) && stristr($_SERVER["HTTP_SAVE_DATA"], "on") !== false) ? true : false;
<html class="<?php if($saveData === true) : echo("save-data"); endif; ?>">