An -ing clause can occupy a place commonly filled by a noun phrase. In Reading maps takes practice, the whole clause reading maps is the subject, while reading remains a verb with maps as its object. The course calls this a gerund-participial clause.
Arriving late is a clause that completes for. The whole prepositional phrase is an adverbial of apologised.
the outer job changes
The same -ing words can build different structures
What job does the same -ing span do in each?
Auditing the ledger is a clause filling the subject slot.
The same words sit inside a progressive predicate after was.
The first sentence uses auditing the ledger as its subject. The second uses the same words inside a progressive predicate. The suffix did not change; the complete unit’s relationship to the larger clause did. That is also why lesson 35’s standing by the gate is a modifier instead of this lesson’s noun-slot clause.
Classify the whole -ing group.
First group the -ing verb with the words that depend on it. Then find the place occupied by that complete group. In She apologised for arriving late, the clause completes the preposition for.
Ten sentences from this lesson, one decision at a time.