saxon:while element is used to iterate while some condition is true.
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element
The boolean expression to be tested.
The condition is given as a boolean expression in the mandatory
attribute. Because this expression must change its value if the loop is to terminate, the
condition will generally reference a variable that is updated somewhere in the loop using
a saxon:assign element. Alternatively, it
may test a condition that is changed by means of a call on an extension function that has