Mention hyphen/dash caveat for boundary symbols

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Review checklist

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Purpose and scope

• [ ] The PR has a single goal that is clear from the PR title and/or description.
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• [ ] No more than 500 lines of code are changed or there is no obvious way to split the PR into multiple PRs.

Code quality

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• [ ] Newly introduced names for variables etc. are self-descriptive and consistent with existing naming conventions.
• [ ] There are no redundancies that can be removed by simple modularization/refactoring.
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Documentation

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Testing

• [ ] The PR passes all tests.
• [ ] New or modified lines of code are covered by tests.
• [ ] New or modified tests run in less then 10 seconds.

Performance

• [ ] There are no type instabilities or memory allocations in performance-critical parts.
• [ ] If the PR intent is to improve performance, before/after time measurements are posted in the PR.

Verification

• [ ] The correctness of the code was verified using appropriate tests.
• [ ] If new equations/methods are added, a convergence test has been run and the results are posted in the PR.

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