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+# Grammar Changes Checklist
+
+This document provides guidelines for making changes to Quarto Markdown syntax.
+
+## 🚨 CRITICAL QUESTION
+
+Before making any grammar change, ask yourself:
+
+**"What existing valid QMD documents might this change break?"**
+
+If you can't confidently answer "none", you need to:
+1. Create test cases for those documents
+2. Run the parser on them before and after your change
+3. Verify they still parse correctly
+
+## When to Use This Checklist
+
+Use this checklist whenever you're adding new syntax to Quarto Markdown, either by tree-sitter changes or changes in the Pandoc AST
+processing steps.
+
+## Pre-Implementation Phase
+
+### 1. Plan Your Test Cases
+
+Before writing any code, plan tests for:
+
+#### Positive Cases (Feature Works)
+- [ ] Basic valid example
+- [ ] Valid example with edge cases (empty, very long, special characters, etc.)
+- [ ] Valid example in different contexts (nested, at start/end of document, etc.)
+
+#### Negative Cases (Similar But Different)
+- [ ] Syntax that looks similar but shouldn't be treated as this feature
+- [ ] Old/deprecated syntax that should be handled differently
+
+#### Edge Cases (Feature in Unexpected Contexts)
+- [ ] Feature appears where it's not expected (e.g., caption without preceding table)
+- [ ] Feature appears between other constructs
+- [ ] Feature appears at document boundaries
+- [ ] Feature appears nested in other constructs
+
+#### Compatibility Cases (Doesn't Break Existing Valid Syntax)
+- [ ] **CRITICAL:** Documents that look like they might conflict with new syntax
+- [ ] Documents with similar punctuation patterns
+- [ ] Documents with similar structure patterns
+
+#### Roundtrip Cases
+- [ ] At least one roundtrip test: QMD → JSON → QMD → JSON
+- [ ] Verify the feature survives roundtripping intact
+
+### 2. Write and Run Failing Tests FIRST
+- [ ] Write test cases in appropriate test directories
+- [ ] Run tests and verify they fail in the expected way
+- [ ] If tests don't fail as expected, revise your understanding
+
+## Implementation Phase
+
+Use your best judgment to implement changes, studying the source code and similar features.
+Ask clarification questions when you conclude that you don't know enough to go on.
+
+### 3. Update Writers If Needed
+
+- [ ] QMD writer (`src/writers/qmd.rs`) - for roundtripping
+- [ ] JSON writer (`src/writers/json.rs`) - if adding new node types
+- [ ] Native writer (`src/writers/native.rs`) - usually auto-handled
+- [ ] Look in the writers/ directory to find others
+
+## Testing Phase
+
+### 4. Run All Tests
+
+- [ ] `cargo check` - verify code compiles
+- [ ] `cargo test` - verify all tests pass
+- [ ] **ALL tests must pass** - don't ignore failures even if they seem unrelated
+
+If you can't write the feature so that your tests pass, do not erase the tests.
+Stop and report them to the user.
+
+### 9. Verify Test Coverage
+
+- [ ] All planned test cases are implemented
+- [ ] Tests are in the appropriate directories:
+  - `tests/snapshots/native/` - for native format output tests
+  - `tests/roundtrip_tests/qmd-json-qmd/` - for roundtrip tests
+  - `tests/pandoc-match-corpus/markdown/` - for Pandoc compatibility tests
+  - `tests/smoke/` - for basic smoke tests
+
+### 10. Manual Testing
+
+- [ ] Test with `-v` flag to see tree-sitter output
+- [ ] Test edge cases interactively
+- [ ] If something unexpected happens, add a test for it
+
+## Quick Reference: Test File Locations
+
+- **Snapshot tests (native format):** `tests/snapshots/native/*.qmd` + `.qmd.snapshot`
+- **Snapshot tests (JSON format):** `tests/snapshots/json/*.qmd` + `.qmd.snapshot`
+- **Snapshot tests (QMD format):** `tests/snapshots/qmd/*.qmd` + `.qmd.snapshot`
+- **Roundtrip tests:** `tests/roundtrip_tests/qmd-json-qmd/*.qmd`
+- **Pandoc compatibility:** `tests/pandoc-match-corpus/markdown/*.qmd`
+- **Smoke tests:** `tests/smoke/*.qmd`
+
+## Remember
+
+The goal is not just to make the feature work, but to make it work **without breaking anything else**.
+
+When in doubt, ask the user for guidance, especially about:
+- Whether there are existing QMD documents to test against
+- How edge cases should be handled
+- Whether a grammar-based or postprocessing-based approach is preferred