`canonical.head`

Default: error
Plugin: canonical

The canonical link is inside <head>.

Why: Search engines ignore a canonical link in <body>.

When off: canonical links anywhere pass.

<!-- ✗ Fails -->
<body>
  <link rel="canonical" href="https://example.com/about/" />
</body>

<!-- ✓ Passes -->
<head>
  <link rel="canonical" href="https://example.com/about/" />
</head>

References

Google: How to specify a canonical URL: Google only accepts a canonical link inside <head>.