The UrlRequest type is used for making HTTP requests in Elm. It is typically used in combination with the Http module to send requests to servers and handle responses. The UrlRequest type allows you to specify the HTTP method, headers, URL, and other parameters needed for the request.
type UrlRequest = Internal Url | External String
All links in an application create a UrlRequest. So when you click <a href="/home">Home</a>, it does not just navigate! It notifies onUrlRequest that the user wants to change the Url. page 
Wiki distinguished between two link forms, internal and external. Internal links received special handling as words with unique meaning to a community. See Context
The wiki global offers plugins an implementation of Collaborative Link called doInternalLink.
The web became more collaborative with wiki's introduction of the Internal Link. Link names were drawn from a shared space backed up at the time by shared storage. Federated wiki's internal links preserves the shared space but not the shared storage making it the ideal link for the distributed collaborative web.
An internal link's Context provides a path to be searched when the link is clicked. The origin, the remote site, the reference cite and forks in the journal all contribute to the context.
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How to extend with wiki-style links? #3 page