link rel="shortcut icon"

rel="shortcut icon" is the spelling Internet Explorer 5 introduced for the “favorites icon” in 1999, before there was a specification for any of it. Every boilerplate of the following decade copied it, and it is still being copied today — usually alongside a second <link rel="icon"> that does the same job.

Why avoid

shortcut is not a link relation. The HTML Standard defines icon and registers the keywords a rel may contain; shortcut is not among them. The rel attribute is a space-separated set of tokens, so a browser parsing shortcut icon finds two tokens, recognises icon, does not recognise shortcut, and discards it. The markup that runs is rel="icon" either way.

That makes the token worse than merely redundant: it is a decision a reader has to make and cannot resolve from the markup. The usual guess is that shortcut is there for old browsers, which is backwards — Internet Explorer accepted plain rel="icon" too, and no browser has ever needed the longer form. So it survives on inertia, and every copy teaches the next author that it is required.

Use instead

Delete the token. Nothing else about the element changes:

<link rel="icon" href="/favicon.ico" sizes="32x32">
<link rel="icon" href="/icon.svg" type="image/svg+xml">

Detectability

Fully detectable. ~= matches one whitespace-separated token, which is exactly how a browser parses rel, so the selector agrees with the parser rather than approximating it. The i flag is load-bearing: link types are ASCII case-insensitive and older boilerplate is full of rel="Shortcut Icon".

The fix removes the single token rather than asserting a new value for rel, so a rel="shortcut icon mask-icon" keeps its mask-icon, and the quoting is left exactly as written — the edit happens inside the delimiter. If shortcut is somehow the only token, no fix is offered: emptying rel would say something different from what the author wrote, and that is a decision for a person.

Resources

• HTML Standard — rel="icon" — the keyword the specification actually defines, and its processing.
• HTML Standard — link types — the registry of permitted rel keywords, which shortcut is absent from.
• Mathias Bynens — rel="shortcut icon" considered harmful — the primary write-up of where the spelling came from and why it is unnecessary.