A MicroStation PickList provides a list of alphanumeric data. They are used primarily when assigning Item Types to an element: the operator can pick a value from a list. It works well, but could be better.
If a PickList were to support multiple columns of data they would become more versatile. For example, suppose a two-column PickList had one column Label and a second column URL. When an Item is added to an element then the Label shows the first column of the PickList. The URL would be used by an application to supplement the Label: it could link to a web-site (e.g. using a DgnLink).
Here's an example PickList having two columns...
Name URL
Door1 http://WeAreDoors/products/doors/door1.htm
Door2 http://WeAreDoors/products/doors/door2.htm
To go even one step further, though it might exceed what we can expect from picklist, we could also look at classification schema's. This is very often used in BIM modelling, for example OBD has a functionality for classification which is integrated in OBD's DataGroup system. But it would be great if that functionality would be made available also for item types because item types are much more versatile for the entire Powerplatform.
To specify what is the difference between such classification and the "simple" two column picklist:
The final "assigned" property is very similar. It contains a first column "Number", for example '03.03.03' and a second column "Description", for example 'Reinforced concrete beams'.
The difference is in the cascading structure of such a classification system:
"03" would be 'Structural elements'
"03.03" would be 'Reinforced concrete'
"03.03.xx" would correspond to 'Reinforced concrete slabs', 'Reinforced concrete columns', ...
Assigning something at the third level inherently means it also is part of that second level, and the first level. This logic is only human interpretation. I don't think there is any software that really knows this, or saves that information to the element.
But upon placing this cascading structure will be shown, like it does really well in the OBD datagroup system. Or in Revit for that matter.