This paper formalizes XML prompting for LLMs as grammar-constrained interactions, leveraging fixed-point semantics and lattice theory. It proves least fixed points for stable protocols (via Knaster-Tarski) and convergence guarantees under a tree metric (Banach-style), ensuring structured, hallucination-free outputs. Includes practical templates like "plan → verify → revise" for human-AI loops, boosting reliability in applications needing parseable data.<grok:render card_id="2276bd" card_type="citation_card" type="render_inline_citation"> <argument name="citation_id">0</argument> </grok:render>