Core concepts

• Architecture — how a query flows to an assessment, and the own-the-logic / source-the-data boundary.

• Regimes — the tax regimes shipped and how they are selected.

• Seller registrations — where the selling entity is established and registered, under which scheme and for which period, and what each of those decides.

• Rate conditions — a category finds the neighbourhood and the conditions on a rate decide the house; how a product is described once so every market can settle them.

• Exemptions — express a buyer certificate natively and get a native Exempt assessment, applied deny-by-default over the regime's verdict.

• Rate breakdown — splitting an assessment's tax across the state/county/city authorities that levy it, with the parts summing exactly to the whole.

• Marketplace facilitator — when the marketplace is liable, the seller charges nothing and still reports the sale.

• Return data — aggregating assessments into per-jurisdiction and per-authority totals for a filing period.

• Dates — the tax point vs the reporting date, and why one date drives every dated lookup in an assessment.

• EU special territories — ten places inside a Member State where its VAT rules do not simply apply, and why a country code is not enough.

• Invoice currency — stating the tax in the place's own currency when the invoice is in another, at the rate for the tax point.

• Public API — what the version number promises, what is internal, and asking the register through TaxRegister.

For task-shaped examples that use these together, see the cookbook.