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Notes on HTTP

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HTTP Specification - RFC 2616

Cache-Control: no-transform

PFWG noted a concern about Cache-Control: no-transform during a review of Guidelines for Web Content Transformation Proxies. This turns out to be a feature of the HTTP specification that WCTP just mirrored. PFWG discussion of Cache-Control: no-transform identified some problems for accessibility with this feature, and acknowledged cases where it needed to be respected in spite of accessibility concerns.

Problems for accessibility:

  • Accessibility transcoding tools core functionality is to do a transformation and need right to do so.
  • Example of transforming star positions into sound - it was a clear situation when the data needed to be transformed.

Reasons Cache-Control: no-transform must be respected:

  • There are things like medical data that needs to be sent end to end with no changes.
  • There are lots of situations where you are accessing via proxies and there is no alternative. You need to have a way to ensure that the data is not being transformed.