If unspecified, inferred from the type of the field.
</st:attribute>
<st:attribute name="default">
If specified, this will be chosen as the default value in case the current selection is null.
If specified, this will be chosen as the default value in case the current selection is null. The default can be an specific instance or a descriptor e.g.
${descriptor.defaultSettingsProvider} or ${descriptor.defaultSettingsProvider.descriptor}. In the later case, the from input fields will be empty.