Annotations are signals that can be sent to search engines for them to better understand the structure of a website and how it relates to other pages or files across the internet. Annotations are hints that give an information but not a directive. As such, annotations are not always respected, especially when they are in contraction with other signals.
The rel attribute of a HTML <link> element establishes a relationship between two URLs. It can be used to specifying the authoritative version of a page, indicating an alternate version for a different device, language or region, etc.
rel="nofollow" tags are used to prevent the flow of equity across certain links. It can help prioritize how bots crawl a site and should be use to separate paid links from the organic search landscape.
Certain search engines, such as Bing, do not support the rel="alternate" hreflang="x" annotations. There are three methods that can be used to help these search engines determine which language is being targeted.