Third-party vendors might be interested in reusing Pane.getConstraint() and Pane.setConstraint() for implementation of custom constraints in their own custom layout classes. Hence I'd like to propose to replace default (i. e. package) visibility by the wider "protected" visibility. While it is unlikely to induce any harm and is fully backwards compatible, it reduces the amount of work for custom implementors and opens a chance for better performance thanks to reuse of already-loaded binary code at runtime.