What do you mean by userFlags and systemFlags in the collection state in MongoDB?

  mongodb, question
[ns] => test.people
 [count] => 47
 [size] => 8
 [avgObjSize] => 0.17021276595745
 [storageSize] => 12
 [numExtents] => 1
 [nindexes] => 1
 [lastExtentSize] => 12
 [paddingFactor] => 1
 [systemFlags] => 1
 [userFlags] => 0
 [totalIndexSize] => 7
 [indexSizes] => Array
 (
 [_id_] => 7
 )
 
 [ok] => 1

Can the expert give a detailed explanation? What are these data respectively, representing the running status of the database, thank you! ! !