Currently the doc says [1] that 0 and false are treated as false.
Actually, off is too.

I would like to request no to be also interpreted as false. (yes being treated as true through the fallback "any other value" case)
Generally speaking, matching what is done in parsing JSON configuration/queries should be nice to have for two reasons (IMHO):

• It makes it more consistent, even though document field values are distinct from ES internal understanding of JSON configuration
• It is good to have multiple english ways to express a false value, as they are very often used internally as values by many programmers (and therefore somehow sent to ES through JSON docs!)

Maybe F would be good too, but for another reason: this is the term being used internally (and people may want to query using it...... ^^)

[1] http://www.elasticsearch.org/guide/reference/mapping/core-types.html