FEEN (Field Expression Encoding Notation) provides a universal, rule-agnostic format for representing board game positions. This gem implements the FEEN Specification v1.0.0 with a modern Ruby interface featuring immutable position objects and functional programming principles. FEEN extends traditional FEN notation to support multiple game systems (chess, shōgi, xiangqi, makruk), cross-style games, multi-dimensional boards, and captured pieces held in reserve. Built on EPIN (piece notation) and SIN (style notation) foundations, FEEN enables canonical position representation across diverse abstract strategy board games. Perfect for game engines, position analysis tools, and hybrid gaming systems requiring comprehensive board state representation.

QPI (Qualified Piece Identifier) implementation for Ruby. Provides a rule-agnostic format for complete piece identification in abstract strategy board games by combining SIN and PIN primitives, with Native/Derived relationship support.