Identifying links to index nodes in HTML output

[Gavin Smith]

I think there should be a more reliable way to identify links to
index nodes from the table of contents in index.html in HTML output.
Currently the only way is to check if "Index" appears in the name of
the page.  This would be used in an "HTML-Info" system, providing the 
functionality of Info using HTML.

Does anybody have any ideas how to do this?  I thought maybe the "rel" 
attribute could be used on the <a> tag.

According to https://developer.mozilla.org/en-US/docs/Web/HTML/Link_types,
the "index" value for the attribute is obsolete since HTML 5, and it 
doesn't mean exactly the right thing:

>Indicates that the page is part of a hierarchical structure and that 
>the hyperlink leads to the top level resource of that structure.
>
>If one or several up link types are also present, the number of these up 
>indicates the depth of the current page in the hierarchy.

This appears to suit the index.html page (i.e. the Top node) better than 
the actual document indices.

But the standard for HTML 4.01 at 
https://www.w3.org/TR/html401/types.html#type-links has a more promising 
description:

> Refers to a document providing an index for the current document.

Maybe it doesn't matter if "index" is used.  I'm not sure if you are 
allowed to use your own values for the "rel" attribute. 
https://www.w3.org/TR/html401/types.html#type-links says you can define 
your own link types and should declare a "meta data profile" if you do 
so, but that standard is out-of-date.

https://www.w3.org/TR/html50/links.html#linkTypes says that you should 
register extensions officially, and conformance checkers would check 
whether the values were registered.  "index" is registered at 
http://microformats.org/wiki/existing-rel-values#HTML5_link_type_extensions
so it should be OK to use.  The description there is appropriate:

>Refers to a document providing a list of topics with pointers that 
>pertain to the current document.

Another idea is to set a "class" attribute on the anchor tag.