[M2] Where to find POM specification?

[Law Green-A20134]

Hi,
 
I have read
http://maven.apache.org/guides/introduction/introduction-to-the-pom.html
, it's pretty simple and clear. But can anyone tell me where to find
detailed POM specification? For I cannot find the information about tags
like "<pluginManagement>" and "<dependencyManagement>".
 
Thanks,
Green