CT = Content Transformation
CP = Content Provider(s)
An entity that is "CT-aware" is assumed to be specifically designed to use or provide CT service per these guidelines.
A "CT proxy" is assumed to be CT-aware. A "non-CT proxy" is assumed to be CT-unaware. Browsers and CP may be CT-aware or CT-unaware.
A CT proxy MAY enable a user or user agent to select preferences for CT service features.
A CT proxy that offers preference selection SHALL be capable of retaining the selections.
When selecting a content representation by default, CT proxies SHALL provide the highest-quality representation compatible with the browser.
"Compatible" in this requirement means a representation that the browser supports, and results in a usable user experience.
A CT proxy SHALL be capable of detecting CT-awareness in CP and browsers.
A CT proxy MAY enable a user to select preferences for user agent identification and capabilities disclosure to CP.
A CT proxy SHALL forward requests to CP without affecting user agent identification or capabilities disclosure, except as necessary to provide a user-selected content representation, or as otherwise specified by user preferences.
A CT proxy SHALL provide availability of the original representation for a CP response.
A CT proxy MAY support local caching of CP responses in their original representation.
A CT proxy SHALL be capable of providing CT service to CT-unaware CP and browsers.
A CT proxy MAY enable a CT-unaware browser user to select a preference for a content representation from among those available through the proxy.
A CT proxy that offers user-selection of content representations SHOULD be capable of user selection of such preferences for specific domains and globally for all domains.
A CT proxy that offers user-selection of content representations SHOULD be capable of offering the user the ability to switch representations when viewing a page.
A CT proxy SHOULD support the ability of a CT-unaware browser user to select the original representation for a CP response.
A CT proxy SHALL support the disclosure of available alternate representations for a CP response to a CT-unaware browser user.
A CT proxy SHALL support the ability of a CT-unaware browser user to select an alternate representation for a CP response.
A CT proxy SHALL recognize and honor CP directives for supported CT services.
As an exception to the previous requirement, a CT proxy SHOULD deny CP directives that would result in dangerous markup being sent to the browser.
A CT proxy MAY enable a user to select preferences for error handing related to CP directives.
A CT proxy SHALL disclose its CT capabilities to CT-aware CP without affecting user agent identification or capabilities disclosure.
A CT proxy SHALL recognize and honor browser directives for supported CT services.
As an exception to the previous requirement, a CT proxy SHOULD deny browser directives that would result in dangerous markup being sent to the browser.
A CT proxy SHALL disclose its CT capabilities to CT-aware browsers without affecting CP-provided headers.
A CT proxy SHALL disclose CT actions taken on CP responses to CT-aware browsers.
A CT proxy SHALL support the disclosure of the original representation for a CP response to a CT-aware browser.
A CT proxy SHALL support the ability of a CT-aware browser to select the original representation for a CP response.
A CT proxy SHALL support the disclosure of available alternate representations for a CP response to a CT-aware browser.
A CT proxy SHALL support the ability of a CT-aware browser to select an alternate representation for a CP response.
A CT proxy SHALL NOT rewrite secure links as a way to enable CT service for those links, without the consent of the CP and user.
A CT proxy that does not support or is not allowed to provide CT service for secure links SHOULD disclose to the user that the CT service will be unavailable for those links.
A CT proxy SHOULD be capable of detecting non-browser user agents.
A CT proxy SHALL be capable of bypassing CT service for detected non-browser user agents.