Case-insensitive regex queries

[muety]

I might be doing something wrong here, but it looks like $regex queries can't be made case-insensitive. Consider the following example.

{
  "selector": {
    "title": {
      "$regexp": "Bar"
    }
}

Having a document with { "title": "Foo Bar Baz" }, the above query will succeed and return the document. However, I'd still like to find it if my regex was bar (lower case).

Using (?i)bar as a regex yield the following error:

Invalid regular expression: /(?i)bar/: Invalid group