If you choose to manage your HTML design outside of the CMS (so put it in the web app instead of publishing it from the CMS) and use the markup.versionedContent helper to output a versioned path to the design files (to ensure that browser cache is not an issue when a new version is released) then you get a blank response. What should happen is the web app should internally strip the version number from the request and rewrite the request to the files within the web application.
So /system/v1.2/assets/css/main.css should rewrite to /system/assets/css/main.css
Similar to how it works when the HTML design is published from the CMS