devd configuration questions

[Sagara Wijetunga]

Hi FreeBSD community 

I have few questions regarding devd configuration: 

1. What is the difference between "attach" or "notify" and when to use them? 

2. What are the possible values for "class" in "attach" and "detach" 
statements? 

3. What are the possible values for "subdevice" in "attach" and "detach" 
statements? 

4. What are the possible values for "system", "subsystem", "type" in 
"notify" statement? 

Kind regards
Sagara