It could be helpful to provide a new operator, similar to $all for arrays, that matches an ordered subset of items:

db.test.insert(

{'actions': [2, 6, 3, 8, 5, 3]}

);
db.test.insert(

{'actions': [6, 4, 2, 8, 4, 3]}

);
// This should find the first document, but not the second as only the first contains [6, 3, 8] in order
db.test.find({'actions': {'$contains': [6, 3, 8]}});

{ "_id" : ObjectId("4b993df679e2022d6d0086f3"), 'actions' : [2, 6, 3, 8, 5, 3] }

A couple of use cases:

• Phrase matching in full-text search (storing stemmed terms as strings in an array)
• Finding users on a website that have performed a certain sequence of actions

Also, allowing it to be optionally anchored to the start or end of an array would open up more possibilities:

• Storing paths to files as individual segments of the path (by splitting the path by '/'), then finding files under a certain directory
  (or more generically, querying on items that have a list that is a path in a tree/hierarchy or a graph).