rails的respond to format

Here are all the default Rails Mime Types:

"*/*"                      => :all
"text/plain"               => :text
"text/html"                => :html 
"application/xhtml+xml"    => :html
"text/javascript"          => :js 
"application/javascript"   => :js 
"application/x-javascript" => :js 
"text/calendar"            => :ics   
"text/csv"                 => :csv   
"application/xml"          => :xml 
"text/xml"                 => :xml 
"application/x-xml"        => :xml 
"text/yaml"                => :yaml 
"application/x-yaml"       => :yaml 
"application/rss+xml"      => :rss   
"application/atom+xml"     => :atom  
"application/json"         => :json 
"text/x-json"              => :json