The Subjectless Passive

Question 1

the werden-passive is often used without a subject to indicate

Answer 1

an activity of some kind is (or is not) taking place.

Question 2

Example

Answer 2

Heute wurde mit den Bauarbeiten begonnen.

Hier daf nicht geraucht werden

Question 3

This construction can be used how?

Answer 3

Any verb, transitive or intransitive.
If no element is placed before the finite verb, the pronoun ‘ES’ is inserted as a dummy subject.
Es wird wieder gekämpft.