[KevinH]

Hi Doitsu,

Wonderful. I have liberally copied and pasted this extra information into my issue on epubcheck, with the hope it clarifies things. They should simply remove that check or accept backlink.

Thanks,

Originally Posted by Doitsu

FYI: when you run EPUCheck with the optional -u/--usage parameter, it'll output the following message:

USAGE(OPF-088): C:/Users/user/Downloads/backlink.epub/OEBPS/Text/Section0001.xhtml(12,116): Unrecognized epub:type value "backlink".

In JSON mode, it'll be:

  "messages" : [ {
    "ID" : "OPF-088",
    "severity" : "USAGE",
    "message" : "Unrecognized epub:type value \"backlink\".",
    "additionalLocations" : 0,
    "locations" : [ {
      "url" : {
        "opaque" : false,
        "hierarchical" : true
      }

(Since it's neither a warning nor an error I mapped it to an INFO message in Sigil.)

If you hear back from the EPUBCheck devs, they'll probably want to know the message code, which is "OPF-088."

Since this message, which is neither a warning nor an error, is only shown if the optional -u/--usage parameter is specified hardly anybody will ever see it anyway.

EDIT: I've just found this 2016(!) post:



(Emphasis mine)