Refactoring effect on internal quality attributes: What haven’t they told you yet?

•(Re-)refactoring occurs in code elements with critical internal quality attributes.•Code elements with many critical attributes are often affected by floss refactoring.•Overall, (re-)refactorings rather improve or keep unaffected than worsen attributes.•Method-level refactoring operations are more likely to worsen many attributes.•Root-canal refactoring outperformed floss refactoring in improving attributes.