4.32. The jb:value Property

If the jb:value property attribute of a binding is not defined when binding key value pairs into maps, the name of the selected node will be used as the map entry key (where the beanClass is a Map). You can also define the jb:value property attribute by putting the "@" character in front of it. The rest of the value then defines the attribute name of the selected node, from which the map key is selected.