The original title is "Why Your Regex Works in Testing But Breaks in Production"

Short summary

A practical guide to common regex bugs that pass testing but fail in production. Covers greedy quantifiers swallowing content, multiline string issues with ^ and $ anchors, and the stateful lastIndex behavior of the g flag in JavaScript. Each issue includes concrete code examples showing the bug and its fix.

• •Greedy .* quantifiers can swallow content between tags — use lazy .*? instead
• •^ and $ match string boundaries by default; use the m flag for multiline input
• •The g flag makes regex stateful via lastIndex, causing alternating true/false results on repeated .test() calls

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