red dot in chrome debugger when writing LESS?

Question

I'm transforming my css files into LESS file.

only part of my LESS is working well and I see a weird red dot line in the chrome debugger for those problematic lines,

any idea what they means?

Answer 1

http://codemirror.net/doc/releases.html says that Version 2.33 of CodeMirror introduced "Show non-printing characters as red dots."