Used to construct a singleton map (one key and one value).
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element
Expression which defines the key of the entry in the new map.
The associated value can be defined either
Available in XSLT 3.0. From Saxon 9.8, available in all editions. Implemented in Saxon-PE and Saxon-EE since Saxon 9.6. Available for all platforms.