Here's the page: http://docs.mongodb.org/master/reference/operator/query/text/#op._S_text

We are currently saying: "A query can specify, at most, one $text expression."

We should be mentioning that a collection can only have one text index, a text query doesn't specify a field (so any field indexed will work), and that when we create a text index, we can specify multiple fields, but we cannot create multiple text indices.