The content_type tag can be used to make the web server send back the contents with the desired Content-Type in the HTTP header.
By default every web page is send back as 'text/html'.
As an example, the RSS feed requires it content type to be set as 'text/xml' for the browsers to properly recognize the feed. The following snippet does the job -
<cms:content_type 'text/xml' />
Please see Core Concepts - RSS Feeds for an example of the usage of this tag.
The desired content type. Some example values are 'text/xml', 'text/plain', 'text/css', 'image/gif', 'application/pdf' and 'application/zip'.
This tag is self-closing and does not set any variables of its own.