What are valid fields for the –format option of git for-each-ref?

I’ve found a field list on git repository, file builtin/for-each-ref.c:

} valid_atom[] = {
    { "refname" },
    { "objecttype" },
    { "objectsize", FIELD_ULONG },
    { "objectname" },
    { "tree" },
    { "parent" },
    { "numparent", FIELD_ULONG },
    { "object" },
    { "type" },
    { "tag" },
    { "author" },
    { "authorname" },
    { "authoremail" },
    { "authordate", FIELD_TIME },
    { "committer" },
    { "committername" },
    { "committeremail" },
    { "committerdate", FIELD_TIME },
    { "tagger" },
    { "taggername" },
    { "taggeremail" },
    { "taggerdate", FIELD_TIME },
    { "creator" },
    { "creatordate", FIELD_TIME },
    { "subject" },
    { "body" },
    { "contents" },
    { "contents:subject" },
    { "contents:body" },
    { "contents:signature" },
    { "upstream" },
    { "symref" },
    { "flag" },
    { "HEAD" },
    { "color" },
};