June 3: Okay in Step 1.
June 4: Difficult and Fail in Step 2.
June 5: success in Step 2.
June 6: fail in Step 3.
June 13: Success in Step 3, but fail in ./tests/step2/valid2.json
June 15:
./tests/step3/invalid.json, in the code is not perfect, and difficult to modify code.<
./tests/step4/invalid.json, it is fail, and don't know how to write the code.
June 17:
"./tests/step4/valid2.json" and "./tests/step3/invalid.json", it is not perfect.
"./tests/step3/invalid.json", the problem is how to distinguish between lower case and upper case.