rb_econv_putbackable  339 include/ruby/encoding.h int rb_econv_putbackable(rb_econv_t *ec);
rb_econv_putbackable 2271 io.c                   putbackable = rb_econv_putbackable(fptr->readconv);
rb_econv_putbackable 4112 transcode.c            n = rb_econv_putbackable(ec);
rb_econv_putbackable 4115 transcode.c            putbackable = rb_econv_putbackable(ec);