MongoDB uses the dot notation to access the elements of an array and to access the fields of a subdocument.
To access an element of an array by the zero-based index position,
concatenate the array name with the dot (.) and zero-based index
position, and enclose in quotes:
'<array>.<index>'To access a field of a subdocument with dot-notation, concatenate the
subdocument name with the dot (.) and the field name, and enclose
in quotes:
'<subdocument>.<field>'