Supported syntax:

• Dice rolls: [N]dM (e.g. 2d20 or d8)
• Decimal integers (e.g. 15)
• Unary operators: +, -
• Binary operators: +, -, *, /, **
• Parentheses for grouping: () (e.g. 2*(d20+1))

Note: The RNG is rather poor, as this relies on JavaScript's own Math.random() — but only for demonstration purposes (final will be server-side).