I wanted to link to 3.0 topic types, hence using https://www.phpbb.com/support/docs/en/3.0/ug/userguide/posting_options/#posting_special as URI. But when you request this URI the JS on that site for unknown reasons redirects to https://www.phpbb.com/support/docs/en/3.0/ug/userguide/special/ which then reads "Error! The section you have requested could not be loaded. Please use the navigation menu on the left to select the section you were trying to reach."

This is annoying and unneeded - my initial URI does lead to excatly what I wanted, but the JS most probably misinterprets it as an "old style" URI. I bet someone forgot that URIs can have anchors at all.