State

Core engine: src/rpn-calculator.js
Active demo: samples/calc-02/ responsive HP48GX layout with HP48-like X-line editing; display-adjacent button row stays in 4 columns
Mode button shows the current angle mode only; selecting a mode uses a popup menu
Public API: push, pop, clear, swap, remove, edit, isValidIndex, input, command, getOperationsByCategory, getConstants
Config: maxSize, base, angleMode, enabledCommands
Commands: arithmetic, stack, trigonometry, constants pi and e
Demo actions: paste now parses clipboard text as a number before pushing it to the stack; Ctrl+V is supported via the hidden input paste event; backspace is ignored when the stack is empty; operation errors are shown as an overlay bar on top of the calculator with a shorter timeout and darker red
Exports: browser window.RpnCalculator, CommonJS module.exports