Mahmud et al 2026: "When Modernization Breaks Working Code: A Single-File Study of LLMs on Legacy PHP" https://arxiv.org/abs/2610.40269 "Pasting a legacy file into an LLM and asking it to 'modernize this' is easy. But is the result better than leaving the code alone? Often, the answer is no. [W]e ask 5 LLMs to modernize 100 WordPress 4.0 PHP files to PHP 8.3 while preserving behavior, with no project context or execution feedback. Each model breaks 32-51 working files while repairing at most 10."