Returns the Mime type for the format used in the request. If there is no format available, the first of the accept types will be used. Examples:

GET /posts/5.xml   | request.format => Mime::XML
GET /posts/5.xhtml | request.format => Mime::HTML
GET /posts/5       | request.format => request.accepts.first (usually Mime::HTML for browsers)

Source Code

# File action_controller/request.rb, line 98
def format
  @format ||= parameters[:format] ? Mime::Type.lookup_by_extension(parameters[:format]) : accepts.first
end