Moreover, AxOutputTransformer was designed to be _behind_ the cache. This patch puts it before the cache. If it is used for anything cacheable, it's purpose wasn't understood.
Not commenting on the patch (which I haven't reviewed sufficiently closely), Matt and I discussed the position of OutputTransformers relative to caching not long after it went in. There are of course good reasons to put it after the cache but there are many cases in which it doesn't make much sense. For instance, given char transcoding at the end of the pipeline (it's implemented as an OutputTransformer) it's a bit silly to perform UTF-8 => Latin-0 conversions for each hit on cached data :)
The conclusion was that there was indeed some value in having AxPreCacheOutputTransformer and AxPostCacheOutputTransformer but neither of us had the tuits or sufficiently felt the itch for that to happen back then.
--robin
