The documentation [XWikiSyntaxLinks] (XWikiSyntaxLinks) contains the description of parameters
I think it would be useful to point out the possible value “title”. This creates a mouse effect: the specified value is temporarily displayed in the browser when the mouse hovers the link.
This is even compatible with the Page Preview Application. With this it is possible to insert HTML code which can contain e.g. images.
However, I don’t think we should list all possibilities as this is not related to XWiki but to HTML and all allowed attributes on the A element. This is probably what we should mention in the doc, possibly with a link to the spec (4.6 Text-level semantics — HTML5). Note that title is a global attribute: 3.2 Elements — HTML5
I am currently creating a modification of the Page Preview Application, in which - if present in the document - the content of an abstract macro is displayed as preview.
{{abstract}}
content to be previewed
{{/abstract}}
In the process, I came across the title specification and checked it for normal links.
I found that the title of the preview popup could be specified.