RFC: Example Rule "Gallery" to showcase CRC best practices?

Following up on some Slack (#autodiff) discussion with @mzgubic, I want to float the idea of adding a CRC rule "gallery" to the ChainRules docs, inspired by analogous things in the plotting world (eg BeautifulMakie).

I think that best practices for rule authors have become a bit too complicated to sufficiently demonstrate with just one or two small examples per section in the docs, particularly with interplay between

• custom structs & their constructors
• higher order functions
• CRC Thunks, Tangent types & AD callbacks

There are many clever rule authors in the wild who post helpful examples on Github/Discourse/Slack/Zulip but this information is very disaggregated and un-searchable. If there were some way for users to submit nice but less ultra-minimal examples and/or to aggregate relevant examples of custom rrule and frule definitions in published packages (as @ToucheSir suggested) I think linking to such a "gallery" from the CR docs would speed up the learning process for rule authors.

I would be glad to help realize such a thing if it seemed feasible and people wanted it.

Less organized thoughts from Slack:
A few custom rule examples I can find in forums but which I wouldn't know how to write based on CR docs:

• Constructors of widely used AbstractArray subtypes like StaticArrays, StructArrays, etc.
• LinearAlgebra methods of “implicit operator” types representing giant Matrices, eg from LinearMaps.jl
• Iterative solver and partial decomposition methods involving the former, eg methods from IterativeSolvers.jl, KrylovKit.jl, Arpack.jl, etc, (“adjoint method” VJP rules)
• Higher order function methods defined outside Base, often versions of map or reduce with parallelism.
• Gradient accumulation into an InplaceableThunk of a custom struct

The issue names no files, tests, or concrete entry point. Start by reviewing the existing ChainRules documentation examples and the linked gallery inspiration, then clarify the gallery's scope and contribution model. Done would require an agreed structure for showcasing custom rrule and frule examples and a decision on how examples from external packages are selected.