I want to add 'subject' and 'news-group' tags to the text events.

Something like:

"#subject":

"#news-group":

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You don't need to prefix them with #, nip12 specifies ways to query arbitrary tags.

tags:[["subject", "blah"], ["news-group","comp.lang.c"]]

filter: ["REQ", "s", {"#subject": ["blah"]}]