由|分隔开的语法叫 alternative pattern.
When importing the first value line ;Hans;admin, the ImpEx extension searches all instances of the Principal type to verify if any instance exists where the uid attribute is set to admin.
Impex extension首先查找所有principal实例，看是否存在其uid属性值为admin的实例。
注意我们现在是试图插入Address数据，如果上述的搜索命中，则将Impex语句里的address值维护到搜索命中的admin Principal实例去。
If an instance exists (and there is, by platform default), the new instance of the Address type has its owner attribute set to a reference to that Principal type instance.
如果并没有Principal实例，其uid属性等于admin，那么进行第二轮搜索，根据AbstractOrder的code字段进行搜索。
Attribute modifier
…;attribute[modifier=value,modifier=value,modifier=value];…
或者
…;attribute[modifier=value][modifier=value][modifier=value];…
The value of the $catalog macro sets the catalog id. The value of the $version macro sets the version string of the catalog version to export.
$catalog=clothescatalog
$version=Staged
宏的实现：
$catalog=catalog(id)
c a t a l o g V e r s i o n = c a t a l o g V e r s i o n ( catalogVersion=catalogVersion(catalogVersion=catalogVersion(catalog,version)
