Nested Markers icons are sorted alphabetically among any regular icons
The moment you click an icon that is a reference to a set of sub-level icons, the content of your Marker section changes accordingly - displaying the Markers from the sub-level folder.
Example
Content of the sample Coding System Nested Codes:
For demonstration purposes, we added a sub folder for each icon, but it is also possible to combine single-level and Multi-level Markers in a single marker system.
Note: The moment a folder is named axactly like a marker icon, it serves as a set of sub-markers.
For example, it is also possible to use this in the 'MedSim' Marker set using a folder 'medication' that holds different types of medication:
During a session, you'll click on the top Code 'Medication':
The moment you click Medication, the icons contained by the sub-folder and representing types of medication appear:
You can of course use more applicable icons for the types of medicine you apply.
▪Now you can pick the applicable type of medicine, for entering into the log file.
The additional arrow 
icon enables you to return to the previous marker-level.