# Expressions

Selectors as Expressions

Every selector is a conditional expression. A selector that evaluates to `true` matches the message; a selector that evaluates to `false` or unknown does not match.

Arithmetic Expression

Arithmetic expressions are composed of numeric literals, identifiers (that evaluate to numeric literals), arithmetic operations, and smaller arithmetic expressions.

Conditional Expression

Conditional expressions are composed of comparison operations, logical operations, and smaller conditional expressions.

Order of Evaluation

Order of evaluation is left-to-right, within precedence levels. Parentheses override this order.

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