[kubanczyk]

I've checked RFC 1738 and it's not the case. The only standard for "+" is:

> (RFC 1866) specifies that space characters should be encoded as `+` in application/x-www-form-urlencoded content-type key-value pairs (see paragraph 8.2.1, subparagraph 1).

From https://stackoverflow.com/a/40292770

[zimpenfish]

RFC1738 is obsolete. RFC1866, referenced in that SO answer, is also obsolete.

But none of that matters, particularly, because lastfm are consuming the URLs, they know full well what "+" means in a URL submitted to their servers, and also they've been around for decades (well before the whole "use %20 instead") - why on earth would they change up their URL scheme when it's working fine?