Types that are not declarable by the user

The following are valid Nushell data types which cannot be declared by the user. They are used by Nushell internally or by plugins or commands compiled in Nushell like Polars and SQLite database.

Besides error values and blocks (see their pages), this group includes custom values such as semver and semver-range (from into semver and into semver-range), matrix (from into matrix), SQLiteDatabase (from open on a SQLite file or stor open), and Polars objects such as polars_dataframe. describe reports their names, but a name like semver cannot be used as a type annotation:

let v: semver = ("1.2.3" | into semver)
# => Error: nu::parser::unknown_type
# =>
# =>   × Unknown type.
# =>    ╭─[repl_entry #1:1:8]
# =>  1 │ let v: semver = ("1.2.3" | into semver)
# =>    ·        ───┬──
# =>    ·           ╰── unknown type
# =>    ╰────

Leave such a variable or parameter unannotated, or annotate it as any.