Use when the user is configuring or extending tax in Spree 6 — tax categories (`tax_code`), tax rates by `country_code`/`state_code`, VAT-inclusive vs added-on pricing (`included_in_price`, market `tax_inclusive`), per-market tax providers and `Spree.default_tax_provider`, writing a custom tax provider (`estimate`/`commit`/`void`/`refund`), `Spree::TaxLine` rows, the `carts.recalculate_totals.set_tax_line_context` hook, B2B tax identifiers (VAT numbers) and exemption certificates, or connecting Avalara/an external tax engine.
