eleventyConfig.addExtension is too case-sensitive #4224

Operating system

macOS Tahoe 26.2

Eleventy

3.1.2

Describe the bug

If I do

eleventyConfig.addExtension("vZome", {...})

I do NOT get processing of files with the extension .vZome. It only processes the files if the argument to addExtension is all lowercase.

This is in contrast with eleventyConfig.addTemplateFormats, which is unaffected by the case of the argument.

Reproduction Source Code URL

No response

Screenshots

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