I don't understand why fixing of this typo should be denied: FExtention is a private variable, i.e. it can be renamed without affecting any user code. SetExtention is private, too - same argument. Only the property Extention is public. But I would simply redeclare it as "Extension" and mark the old one as "deprecated" - this way users see a warning and have a grace period during the next released version to adjust their code (and knowing the release cycles of FPC this will take several years).