[TXyy2023]

The DRY example uses ($a.len(),) and ($b.len(),) in its assertion message without explaining the trailing commas. This adds a short note identifying the single-element tuples, showing their effect on the formatted lengths, and linking to the tuple and macro-repetition chapters. The runnable example is unchanged.

Fixes #1955.

Validation:

• Compiled and ran the original example's three tests.
• Verified the actual length-mismatch message with 2- and 3-element vectors; a scalar control confirms that the tuples affect formatting, while the assertion still compares lengths directly.
• mdbook test (197 chapters), builds for English/Japanese/Chinese/Spanish/Korean, and the official Rust full-tree linkchecker for all five builds.
• git diff --check; rendered prose and local links checked.

AI disclosure: This contribution was prepared and validated with OpenAI Codex in a user-authorized automation.

[rustbot]

Thanks for the pull request, and welcome! The Rust Project has assigned @marioidival (or someone else) to review your changes, you should hear from them (or someone else) within the next two weeks.

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @marioidival

[jieyouxu]

Hi there,

This looks like an automated submission, which is not permitted.

We are thus suspending you as per our policies [1], [2] and contribution standards [3]. You can contact the moderation team to discuss and possibly reconsider your suspension.

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