FEEN (Forsyth—Edwards Enhanced 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.

Parse and generate Portable Action Notation (PAN) strings for representing atomic actions in abstract strategy board games including chess, shogi, xiangqi, and others. PAN provides an intuitive operator-based syntax with six core operators: "-" (move to empty square), "+" (capture), "~" (special moves with side effects), "*" (drop to board), "." (drop with capture), and "=" (in-place transformation), plus "..." (pass turn). Supports coordinates via CELL specification and piece identifiers via EPIN specification. Handles transformations ("e7-e8=Q"), enhanced/diminished states ("+R", "-P"), and style derivation markers ("K'"). Provides comprehensive validation, immutable action objects, and functional API design. Examples: "e2-e4" (move), "d1+f3" (capture), "e1~g1" (castling), "P*e5" (drop), "e7-e8=Q" (promotion), "..." (pass), "+d4" (static capture), "e4=+P" (modify).