# Diagnostic underline styling

**URL:** <https://discuss.codemirror.net/t/diagnostic-underline-styling/9892>\
**Category:** Uncategorized\
**Created:** [September 23, 2026, 3:52pm UTC](https://discuss.codemirror.net/t/diagnostic-underline-styling/9892 "2026-09-23T15:52:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![benniekiss](https://discuss.codemirror.net/user_avatar/discuss.codemirror.net/benniekiss/32/5333_2.png) [@benniekiss](https://discuss.codemirror.net/u/benniekiss)\
**Post date:** [September 23, 2026, 3:52pm UTC](https://discuss.codemirror.net/t/diagnostic-underline-styling/9892/1 "2026-09-23T15:52:54Z")

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Currently, codemirror diagnostics are styled with a generated svg underline, and I was wondering if there was a reason to do this, rather than using the browser’s native CSS styling.

I ask since a Zettlr (markdown texteditor using CM6) user has reported they experienced noticeable performance improvements by removing the svg-generated underlines. I’d be interested in implementing this app-wide, but I was curious about the rationale before doing so.

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**Author:** ![marijn](https://discuss.codemirror.net/user_avatar/discuss.codemirror.net/marijn/32/136_2.png) [@marijn](https://discuss.codemirror.net/u/marijn)\
**Post date:** [September 23, 2026, 4:37pm UTC](https://discuss.codemirror.net/t/diagnostic-underline-styling/9892/2 "2026-09-23T16:37:32Z")

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If I am not mistaken, Safari has only gotten support for wavy underlines last year, and CodeMirror aims to also work on browsers older than that. Hence the use of SVG by default. But of course you’re welcome to override that if you target only evergreen browsers.

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**Author:** ![benniekiss](https://discuss.codemirror.net/user_avatar/discuss.codemirror.net/benniekiss/32/5333_2.png) [@benniekiss](https://discuss.codemirror.net/u/benniekiss)\
**Post date:** [September 23, 2026, 5:33pm UTC](https://discuss.codemirror.net/t/diagnostic-underline-styling/9892/3 "2026-09-23T17:33:31Z")

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This is good to hear! Zettlr is electron based, so very evergreen 😛 I’m looking at when the spelling underlines were supported, and its surprisingly recent for all browsers, like within \<2 years for all of them. Regardless, thank you for the quick response! I think using the native css will offer a nice performance boost for the app