rb_econv_putbackable  254 include/ruby/encoding.h int rb_econv_putbackable(rb_econv_t *ec);
rb_econv_putbackable 1558 io.c                   putbackable = rb_econv_putbackable(fptr->readconv);
rb_econv_putbackable 3777 transcode.c            n = rb_econv_putbackable(ec);
rb_econv_putbackable 3780 transcode.c            putbackable = rb_econv_putbackable(ec);