How PX-Backup achieve the application-consistent backups

Dear PX-Backup Community Team,

I have gone through with PX-backup " Application consistent backups" published on URL:

I am intersted in knowing how PX-backup implements the quiesceing machenism while taking snapshot during backup.
Somewhere i also read that volume level quiesceing is also provided through PX backup.

Objective of asking the above query is to understand the idea "how the overall backup constency (Either at Application level or at volume Level) feature is designed.