When using ${labels.item.value.true} or ${labels.item.value.false} in a component in my zul file to get my labels from properties 118n files, if the files contains the following values:
item.value.true=True
item.value.false=False

I receive one of the following errors:
org.zkoss.xel.XelException: Encountered "true", expected one of [<IDENTIFIER>]
org.zkoss.xel.XelException: Encountered "false", expected one of [<IDENTIFIER>]

A workaround is to use the old (<=5.0.7 versions) notation
${c:l('item.value.true')}
${c:l('item.value.false')}