Constants are used throughout the shop for consistent naming for price related request and response values.
All the constants for price engine are stored in final class:
|source of price calculation e.g. ERP, Shop, Request|
|type of price e.g. list, custom, base|
|type of price line e.g. product, shipping|
|type of total value e.g. sum, lines, additional_lines|
|indicates which price provider calculated the prices|