It seems reasonable that if dot-notation works as a field-selector when selecting object members, that it should also work when selecting array indexes,
but that doesn't seem to be the case with the current version of MongoDB.
The second command fails to return anything. You can in fact use the $slice operator to get the element, but then the command becomes large and ugly:
When developing custom ORM classes to access Mongo, this special case will be needed when accessing an array element by index. This seems unnecessary.
I suggest that Mongo handle dot-notation the same for Arrays as it already does for Objects, and simply allow you to select by index. (Note, that a find query does allow array indexes in the dot notation, but the field select param does not)