While Qt Designer doesn't care about casing, the XML schema spec does.
Due to Qt Creator automatically changing case on save, require the
uppercase variant in all situations, so that other devs don't have to
manually change the case after Qt Creator changes it.
NOTE: This introduces an adjustment to the spec, different from what
Qt provide from Qt Designer. If this file is changed in future, this
diff may need to be manually re-applied.
https://doc.qt.io/qt-5/designer-ui-file-format.html
923d427212