Current feature:
zul.inp.InputWidget.select()
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/inp/InputWidget.js#L294

The actual selection is performed with

.setSelectionRange()
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/inp/InputWidget.js#L300

Since those are 1-to-1 html standard methods implemented for ZK, with some QoL differences between select and setSelectionRange (FF doesn't use the same state for these 2 methods for example), it would make sense to use the html select() as basis for zk select()
https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement/setSelectionRange
https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement/select