Web links are text links that open in a web browser if followed from within Tinderbox. As well as web pages, a URL link can act as a 'mailto:' call or link to local files (using the 'file:///' protocol instead of 'http://'). Basically, a valid URI.
In all cases Finder will dictate whether a browser or some other application, such as a mail client is used to open the URL. This can also be used to use app pseudo-protocols such as are provided by apps like DEVONThink to allow linking to items stored within the app.
The Create Link dialog includes a few extra inputs only pertinent to web links, as these are used during HTML export as HTML link parameters.
The same extra data can also be viewed/edited in the Browse Links dialog.
A web link cannot be created at note level (i.e. as in a basic link) but setting the $URL attribute is akin to doing this. If more than one such 'link' is needed, the user should add extra URL-type user attributes.
The Substitutions menu, smart links can be used to make RTF web links in $Text but whilst these can be used to open web links (or other protocols as above) these links are not recognised by Tinderbox as the they are only embedded in the RTF text.
Note that export code ^outboundWebLinks^ only lists actual Tinderbox web links and not URL-type attributes or smart links