[FR]: Tag functionality based on `<category>` (different from the "label" system)

[RuanJintao]

Brief description of the feature request

When browsing some RSS feeds, many sources have tags represented by <category> to classify articles, similar to how Pixiv uses tags. However, I couldn't find this interface when using it; the only place I discovered this feature being used is in custom filters. This feature, which can be referenced from QuiteRSS—this software displays tags in the header section—would make searching, categorizing, and reading more convenient if it could be added.

[martinrotter]

This is already possible and integrated into article filtering mechanism. RSS Guard automatically extracts "categories" from all supported formats (ATOM, RSS, RDF, JSON) and they are available to article filtering system.

https://rssguard.readthedocs.io/en/stable/features/filters.html#functions

You can easily extract found "categories" to RSS Guard labels to have them easily available.

/*
 * Automatically create RSS Guard labels for all article categories defined for this article in a feed source.
 * 
 * This supports RSS, ATOM and JSON category standards.
 */
function filterMessage() {
  msg.exportCategoriesToLabels(true);
  return Msg.Accept;
}

[martinrotter]

After all enabled feeds are fetched, the list of labels will be (re)populated. The feature is smart and reuses all existing labels across whole "profile" allowing you to use single label with same name across all your feeds.

Then you can of course filter, search your articles with tag name etc.

I do not plan adding simple checkbox to enable the feature at this time.