Custom loader markdown clarity

[paul-sachs]

The docs read to me as if whether you're using a custom loader (inline or otherwise), there's a way to access the rendered content but this is only the case with the glob or file loaders. Currently, custom loaders need a lot more additional logic in order to leverage the markdown processor to move local files externally and match behaviour.

Either we should modify docs to make that obvious or we should add some utilities to the loader to make grabbing the markdown processor much easier.

[paul-sachs]

I suspect part of the confusion is due to expanding content collections to include external sources. This line here says that it's not built into anything but content collections, but now that content collections seem to include custom loaders, maybe just a little more clarity there would be sufficient?