rb_econv_set_replacement  318 include/ruby/encoding.h int rb_econv_set_replacement(rb_econv_t *ec, const unsigned char *str, size_t len, const char *encname);
rb_econv_set_replacement 2597 transcode.c            ret = rb_econv_set_replacement(ec,
rb_econv_set_replacement 4211 transcode.c        ret = rb_econv_set_replacement(ec,