# State
- Core engine: `src/rpn-calculator.js`
- Default demo: `samples/dev/` classic browser demo; `samples/calc-02/` remains the portrait-first HP48GX-inspired reference
- Public API: `push`, `pop`, `clear`, `swap`, `remove`, `edit`, `isValidIndex`, `input`, `command`, `getOperationsByCategory`, `getConstants`, `listConstants`, `setConstant`, `removeConstant`, `hasConstant`
- Config: `maxSize`, `base`, `angleMode`, `enabledCommands`
- Commands: arithmetic, stack, trigonometry, constants `pi`, `e`, `phi`, `g`, and `c`; arithmetic includes `root` with `y√x`, `yroot`, and `nroot` aliases; constants can be added or removed dynamically through the core API
- Demo behavior: `samples/dev/` keeps hidden input focus on desktop and supports clipboard paste; `samples/calc-02/` uses compact mode/constants popups, a 4-column display-adjacent row, stack selection/move mode, and paste through the hidden input
- Exports: browser `window.RpnCalculator`, CommonJS `module.exports`