An essential relative clause provides necessary, defining information about the noun. On the other hand, non‐ essential relative clauses provide additional, non‐necessary information about the noun.

In this case, ‘Not until I saw what happened’ is the adverbial clause. The inversion takes place after this, in the main clause. This happens with 'Not +time' and 'Only + time'.

Inside the house (An adverbial) Making a chair with bamboo (A phrase with a gerund) On the other hand, a clause is an expression/a group of words with a subject and a predicate.

Adverbial clauses are identifiable because they begin with subordinating conjunctions, namely, ‘unless’ ‘after’, ‘if’, ‘because’ and ‘although’ etcetera.

A fronted adverbial is when the adverbial word or phrase is moved to the front of the sentence, before the verb. Earlier today, I discovered fronted adverbials.