Some standard rendering mechanisms are already defined, but the system lets the set of rendering mechanisms be expanded, allowing for:

• Additional standard rendering mechanisms to be defined in the future
  
• Application definition of private or nonstandard rendering mechanisms

An application can elect to support some, all, or none of the standard rendering mechanisms defined by the system. Applications that do not support any of the standard rendering mechanisms are not precluded from using direct manipulation. However, support of the standard rendering mechanisms and formats increases the chances of a successful data transfer between applications.

An application that supports a particular rendering mechanism, whether or not it is a rendering mechanism defined by the system, must follow a specific set of guidelines defined by that rendering mechanism, including conversation-initiation procedures and naming conventions.