Simply put, it is used with the perfect subjunctive in subordinate clauses.

The same frequently occurs in elliptical clauses beginning with as.

Of the two, only which is commonly used in non-restrictive clauses.

In active clauses, the subject is the agent responsible for performing the action.

But it's a good idea to state the position explicitly in separate clauses of employees' contracts.

The causative is also used in main clauses to imply some underlying cause.

In most imperative clauses the subject is absent: Eat your dinner!

The connegative is a word form used in negative clauses.

On the other hand, the satellite only occurs in clauses.

When Nicole finally caught her breath, she spoke in short, broken clauses.