The documentation for QString.isUpper() on the website says: "Returns true if the string is uppercase, that is, it's identical to its toUpper() folding."

However, this is not how it is documented nor implemented in the source code: "Returns true if the string only contains uppercase letters, otherwise returns false."

Even though the implementation described on the website makes more sense, it is indeed implemented such that QString("3").isUpper() will return false.

The method QString.isLower() has the same issue.