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+---
+epic: 8
+story: 8.3
+title: "Syntax Highlighting"
+status: draft
+---
+
+## Epic 8 — Windows App (Rust + iced)
+**Goal:** Fast, lightweight native Windows app -- single .exe, no runtime dependencies.
+
+### Story 8.3: Syntax Highlighting
+
+As a **Windows user**,
+I want syntax highlighting in the editor that colors numbers, operators, units, variables, comments, and errors,
+So that I can visually parse my calculations quickly.
+
+**Acceptance Criteria:**
+
+**Given** the user types `total_cost = $1250 + $300 // monthly`
+**When** the text is rendered
+**Then** `total_cost` is colored as a variable, `=` and `+` as operators, `$1250` and `$300` as numbers/currency, and `// monthly` as a comment
+
+**Given** the user types an expression that produces an error
+**When** the text is rendered
+**Then** the erroneous portion is highlighted with an error indicator (e.g., red underline or distinct color)
+
+**Given** the Windows system theme is Light mode
+**When** the editor renders
+**Then** syntax colors have sufficient contrast on a light background
+
+**Given** the Windows system theme is Dark mode
+**When** the editor renders
+**Then** syntax colors have sufficient contrast on a dark background
+
+**Given** the syntax highlighting is implemented
+**When** colors are applied to text spans
+**Then** the engine tokenizer provides the span boundaries and token types, and the iced text renderer applies corresponding colors