rel="icon"
Defines a resource for representing the page in the user interface, usually an icon (auditory or visual one).
The media, type and sizes attributes allow the browser to select the most appropriate icon in its context. If several resources match, the browser will select the last one declared, in tree order. As these attributes are merely hints, and the resources may be non-appropriate upon further inspection, the browser will then select another one, if appropriate.
Note: Apple's iOS do not use this link type, nor the sizes attribute, like others mobile browsers do, to select a webpage icon for Web Clip or a start-up placeholder. Instead it uses the non-standard apple-touch-icon and apple-touch-startup-image respectively.
The shortcut link type is often seen before icon, but this link type is non-conforming, ignored and web authors must not use it anymore.
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https://developer.mozilla.org/fr/docs/Web/HTML/Link_types