From http://docs.mongodb.org/manual/reference/limits/#limit-index-size

"Indexed items can be no larger than 1024 bytes. This value is the indexed content (i.e. the field value, or compound field value.)"

The above is not true. The below is closer to true, from http://docs.mongodb.org/manual/core/indexes/#index-behaviors-and-limitations

"Index keys can be no larger than 1024 bytes. This includes the field value or values, the field name or names, and the namespace."

Last time I tried, there was an off-by-some error in the docs for the hard cutoff of this limit, so I'm still not quite trusting the above. I suggest we provide a formula from which users can calculate the maximum size field value for a given index, so they can ensure that they never insert values greater than this limit.