HTML: How 8 elements create 31+2 kinds of metadata
The 8 metadata elements in HTML are base, link, meta, noscript, script, style, template, and title.
base, style, template, and title creates one metadata respectively; link creates 10 standard metadata and any custom link; meta creates 13 standard metadata and any custom meta; noscript does not create metadata but modifies some metadata; and script creates 4 metadata. In total, that's 31 standard metadata and 2 custom metadata.
How link element creates 10+1 standard metadata
A link element accepts sixteen local attributes. Only rel attribute creates metadata but all attributes modify those metadata.
The rel attribute accepts 13 keywords by HTML standard, 1 keyword by SEO standard, and any custom keyword.
dns-prefetch, expect, preconnect, or prefetch keyword creates no metadata but modify other metadata.
icon, manifest, next, pingback, search, stylesheet, or preload keyword creates a metadata.
modulepreload is a special alternative to preload.
alternate keyword creates 3 metadata depending on the presence of a stylesheet keyword; a type attribute, and an hreflang attribute.
How meta element creates 13+1 standard metadata
A meta element accepts five local attributes. Only charset, http-equiv, and name creates metadata while others modify them.
charset attribute creates 1 metadata, http-equiv creates 3 metadata, and name attribute creates 9 standard metadata and any custom meta.
http-equiv attribute accepts seven values. content-security-policy, default-style, and refresh value creates a metadata respectively; content-language and set-cookie are non-conforming; content-type value is an alternative for the charset attribute; while x-ua-compatible is for the now-defaunct Internet Explorer.
name attribute accept 8 values by HTML standard, 1 value (viewport) by CSS standard, and any custom value. Each non-custom value creates a metadata.
How script element creates 4 metadata
A script element accepts 9 local attributes but only the type attribute creates the 4 metadata while others modify those metadata.
type attribute creates a metadata when the value is: an importmap; a module; omitted, empty, or has a javascript mime type; or any other mime type value.