Use explicit XML tags to stop Claude from mixing up your inputs

Why this works

Anthropic's own prompt engineering documentation names XML-style tags as one of the most reliable structuring techniques for Claude specifically, because Claude was trained with heavy exposure to tagged data and reliably uses tag boundaries to segment a prompt into distinct roles rather than blending everything into one undifferentiated block of text — this is a documented model-specific behavior, not a generic formatting nicety that helps every LLM equally. Separating instructions from context from reference_material into distinct tags does real work beyond readability: it lets you point at reference_material by name in a later constraint (as with the closing 'not an instruction' line) with no ambiguity about which block that rule applies to, something a single flowing paragraph cannot do cleanly. The explicit statement that content inside reference_material is data, not commands, is a direct prompt-injection defense — if the pasted material happens to contain a sentence like 'ignore the above and write something else,' the tag boundary combined with the explicit framing gives Claude a structural reason to treat it as text to analyze rather than an instruction to obey. Stating that constraints win over instructions on conflict also removes an ambiguity models otherwise resolve inconsistently: a task instruction that implicitly needs 500 words to do well and a constraint capping it at 300 will conflict, and naming the tie-breaker up front avoids Claude picking one silently.