$ cd JSON-Parse-0.40
$ grep -r "warn_only" *

Json3.xs:warn_only (parser, onoff)
Json3.xs:	parser->warn_only = SvTRUE (onoff) ? 1 : 0;
json-common.c:    unsigned int warn_only : 1;
json-entry-points.c:    parser_o.warn_only = 1;
lib/JSON/Parse.pod:=head2 warn_only

##</code><code>##

void
warn_only (parser, onoff)
    JSON::Parse parser;
    SV * onoff;
CODE:
    parser->warn_only = SvTRUE (onoff) ? 1 : 0;