On 2011-03-05 <19:33:45>, Cecil Westerhof wrote:
> At http://wiki.contextgarden.net/Reference/en/useURL there is a description
> of useURL. I am using it for HTTP and e-mail referencing. But I do not
> understand where the third parameter is used for,

There’s a minimal explanation added by Taco a while ago to [1].
Appears to be legacy syntax by now.