How to understand the `%` in KDE's syntax-highlighting code

I am the author of VNote, which uses KDE's Syntax-Highlighting lib.

After updated the version of the lib, I found that there is a new file ansihighlighter.cpp and it uses % to concatenate a QLatin1Char and a QString. Qt6 complains that % operator for this is not defined.

So how to understand this operator here? I could not find the definition of this operator.

https://github.com/KDE/syntax-highlighting/blob/79a21485c9730e20e2ddcf06ab80a935480d04fc/src/lib/ansihighlighter.cpp#L930

Thanks!