Understanding the dynamic mode of mongodb document

I have already learned ,mongodb Document corresponding to RDBMS The line of ; The difference is ,

The document has a dynamic mode ; That is, documents in the same collection do not need to have the same fields , Even the same field can be of different types ;

The above has been inserted in the assembly village 2 Documents , Next insert a , The number and type of fields are the same as before 2 Different article ;

Insert a , And display as follows ;