Vue version

3.2.39

Link to minimal reproduction

https://github.com/n1c/vue-renderToString-lowercase-props

Steps to reproduce

npm install
node index.js

What is expected?

The template of <svg viewBox="0 0 10 10"></svg> is expected to render exactly as such.

What is actually happening?

Template is rendered as: <svg viewbox="0 0 10 10"></svg> ("viewbox" is now lowercase).

This breaks SVG's when used in an img tag. e.g. <img src="../../image.svg" />

MDN docs have the case as "viewBox": https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/viewBox

System Info

System:
    OS: macOS 12.6
    CPU: (4) x64 Intel(R) Core(TM) i5-5350U CPU @ 1.80GHz
    Memory: 16.78 MB / 8.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 18.9.0 - /usr/local/bin/node
    npm: 8.19.2 - /usr/local/bin/npm
  Browsers:
    Chrome: 105.0.5195.125
    Safari: 16.0
  npmPackages:
    vue: ^3.2.39 => 3.2.39

Any additional comments?

Bumped into this while working on https://vue3-avataaars.com/

Specifically the svg's work great as a component, but cause issues when used as an image e.g. <img src="https://vue3-avataaars.com/random-svg" />

The bundlers are lowercasing keys they don't recognize:

By adding viewBox to the propsToAttrMap const in all the renderers, the toLowerCase() is skipped and you get the output you need:

If it were possible to extend that propsToAttrMap at runtime, this would be solvable, I reckon?

Much appreciated Evan 🙏