hreflang="vo"

vo is a valid hreflang value for Volapük.

Language: Volapük (vo, ISO 639-1)

Example

<link rel="alternate" hreflang="vo" href="https://example.com/vo/" />

The code is case-insensitive for Google. The conventional spelling is a lowercase language, a title-case script and an uppercase region: vo.

Without a region, the annotation targets every Volapük speaker regardless of country. Regional versions sit next to the language-only version in one cluster.