The Languide high-level command C-insert f (languide-convert-region-to-function) has converted the selection into a function, and replaced it with a call to the new function. A framework for another call to the function is placed on the kill-ring, as this operation is typically done with the aim of re-using code. Until the next keystroke, changes like this are highlighted differently, as they can take place some distance from the selection and it can otherwise be hard for the user to spot exactly what Languide has done.