rb_hash_lookup2   485 hash.c             return rb_hash_lookup2(hash, key, Qnil);
rb_hash_lookup2   380 include/ruby/intern.h VALUE rb_hash_lookup2(VALUE, VALUE, VALUE);
rb_hash_lookup2  3956 io.c           	v = rb_hash_lookup2(opt, sym_encoding, Qnil);
rb_hash_lookup2  3958 io.c           	v = rb_hash_lookup2(opt, sym_extenc, Qundef);
rb_hash_lookup2  3960 io.c           	v = rb_hash_lookup2(opt, sym_intenc, Qundef);