6. Experimental Media Type Values
Media type values beginning with the character string "X-" are reserved for experimental purposes.
Naming Conventions
Experimental types:
X-my-experimental-type
x-custom-format
Experimental subtypes:
text/x-custom
application/x-my-app
Usage Recommendations
- For testing only: Experimental types should not be used in production environments
- No standardization guarantee: These types are not managed by IANA
- Possible conflicts: Different organizations may use the same X-prefix names
- Transition to standard: Successful experiments should be registered as official types
Considerations
Historically, the X-prefix was widely used, but is now deprecated:
- RFC 6648 deprecated the X-prefix convention
- New experimental types should use vendor prefixes (vnd.)
- Or register directly as standard types
Modern Practice:
- ❌ Not recommended:
application/x-custom - ✅ Recommended:
application/vnd.company.custom(after registration) - ✅ Recommended: Register standard subtypes directly