Global counter for cross-referenceable figures, tables, code listings, etc

[vccortez]

Description

I'd like to suggest having a project-wide counter for cross-referenceable items such as figures and tables that would allow cross-document referencing by default. This would allow us to reference a figure from another document using the regular @fig-* syntax and have a functioning link to that particular cross-referenceable item show up with its project-wide number.

In other words, the moment you add a referenceable item to a page, that item would also get a project-wide unique number that would be used whenever it gets refereced from another document. Currently, it seems cross-document references are not implemented or understood in website projects, even though they work in book projects.

Personally, I don't quite understand why cross-document references should not work in website projects by default. I was expecting to get a simple working hyperlink, which websites are all about, to another page's figure. If the issue is not having an clear numbering for it to reference, a project-wide counter feels like a safe bet, considering even books and manuscripts implement this type of numbering for their lists of figures or tables indices.