The subject "Classify" has different aspects. Following table shall give an overview on this. When following links you will reach respective insertion points.
Practical examples
Point of reference
Placement information
Meta information (e.g. Electrical engineering, Piping)
CNS
Order number
Type code
etc.
Standards
eCl@ss
By Categories, By Countries, By Alphabet
Standard parts
(Placement dialog)
Connection elements
Electrical engineering
BIM
Piping
Part (standard for most of classifications)
Connection point (published elements) [especially at CNS classification]
single variable
Project level
Directory level
Add projects to classification
Batch classification of projects
Other cross cutting issues:
Create own class system
Map class systems...
Collect classification data...