ArionFX is much more than just a tonemapping operator plug-in. It is a very complete HDR image post-processing toolset.
By the name ArionFX toolchain we refer to the list of consecutive stages, or components, that form the ArionFX filter.
All stages are optional, and are arranged in a way that ensures that the input floating-point information is carried correctly from beginning to end, with no loss.
Internally, some effects must be applied before Tonemapping, in High Dynamic Range (e.g., Despeckler, Bloom, Glare...), while some effects must be applied after Tonemapping, in Low Dynamic Range (e.g., Sharpen, Grading...).
The tabs in the UI reflect the order in which said stages are applied.
Lens glare applied after Tonemapping.
Lens glare applied before Tonemapping.