Clarify that the 'language' field can only be used in the root of a document.

On CS-18520 a customer wanted to created sub documents with a

{language}

field.

We did some test and found that its not possible:

> db.testCollection.ensureIndex(

{ "$**": "text" }

,

{ name: "TextIndex", language_override: "newdoc.language" }

)
{
"errmsg": "exception: language_override is not valid",
"code": 17136,
"ok": 0
}

The docs don't explicitly say that this is not allowed:

http://docs.mongodb.org/manual/tutorial/specify-language-for-text-index/#specify-the-default-language-for-a-text-index

Also, the internal wiki page on text indexes is very helpful. Could we incorporate the examples from the wiki into the public docs:

https://wiki.mongodb.com/display/KB/FAQ%3A+Creating+a+text+index+and+searching+words+and+phrases

-Annette