COSESAI

ISO 8601 Duration Builder Field Guide: When PnYnMnDTnHnMnS Rules The Time Interval Grammar

By xiezixing 2026年8月29日

A field guide to the ISO 8601 PnYnMnDTnHnMnS duration grammar, with the four edge cases that ruin most naive parsers and the four programming stacks that implement months four different ways.

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Accessibility Checker Field Guide: When WCAG 2.1 Compliance Should Not Be a Friday Night Audit

By xiezixing 2026年8月28日

WCAG 2.1 does not fail loudly. A button can render, an image can display, and…

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Data URI Generator Field Guide: When Inlining Beats A Request And When A File Wins

By xiezixing 2026年8月28日

A field guide to the break-even line for Data URIs inlining in production frontends. Covers the three rules that decide when inlining wins, the five pitfalls that quietly break the deal, and the audit pass that catches them before CSS ships.

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Unicode Escape Converter Field Guide: When Four Escape Styles Beat One Universal Form

By xiezixing 2026年8月28日

Eighteen hex and Unicode escape pairs sit in your clipboard, and a single NFD-vs-NFC mismatch…

Underline Text Field Guide: When One Invisible Combining Mark Replaces HTML

By xiezixing 2026年8月28日

Combining low line is a single Unicode codepoint, U+0332, that draws a line under the…

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Pangram Checker Field Guide: When The 26-Letter Set Sits Inside One Sentence

By xiezixing 2026年8月28日

A field guide to using the [Pangram Checker](https://elysiatools.com/en/tools/pangram-checker) for typography specimens, cipher keys, classroom worksheets, and QA fixtures.

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JWT Inspector & Verifier Field Guide: When Decoding Is Not Verifying

By xiezixing 2026年8月28日

Decode, verify, and rehearse the algorithm-confusion attack on JWTs. The seven claims that decide whether your verifier admits or rejects a token.

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PDF/A Validate Field Guide: When Four Pre-Flight Checks Beat a Single Conformance Run

By xiezixing 2026年8月27日

PDF/A is a constrained subset of PDF designed for long-term preservation. This field guide walks through the four pre-flight checks (XMP metadata, encryption, font embedding, forbidden features) that decide whether a document will pass a real archival conformance test before you ever upload it to VeraPDF.

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Leet Speak Converter — Field Guide: When 1337 Spelling Survives the Decade When the Substitution Tables Were

By xiezixing 2026年8月27日

Leet speak is a single, simple, completely reversible substitution cipher hiding inside what looks like…

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Image Resizer Field Guide — When Three Resize Modes Beat a Single Resize Button

By xiezixing 2026年8月26日

Three resize modes, five output formats, and one decision that prevents 90% of blurry thumbnails.…