Every grandparent should seek out and sing the perfect nursery rhyme appropriate to their particular tiny grand-offspring so that they can participate in actions and noises. By trial and error, I found it yesterday: 'Knees up Mother Brown'. ('HEY!!!')
As 'Zeyde' (Yiddish for grandfather) it will be my duty to pass on:
Herrel Shmerel went to the races
lost his gatkes and his braces.
(Herrel = little chap; shmerel = fool; gatkes either means long johns or trousers.)
Granny's in the kitchen
Doing a bit of stitching
In came the bogeyman
and chased Granny out.
BOO!
Well, said the bogeyman,
that's not fair!
Well, said Granny,
I don't CARE!
In the 1950s and 60s, there was a small group of former teachers, inspectors, teacher trainers - probably no more than 20, possibly less, who made huge stacks of dosh writing text books year after year after year. Remember them?
Here is 'main clause': 'I ate a bun.' If I put a) 'Happily', or b) 'In the morning' or c) 'When I got up' in front or before 'I ate a bun', it's a fronted adverbial. (a) is an adverb, b) is an adverbial phrase, c) is an adverbial clause.
1. Why has this feature of sentence structure been singled out for special mention? There is no answer to this question from grammarians. An 'adverbial' can come after a 'main clause'. Why not identify and name this? No answer.
2. My point is that this bit of terminology is random and even by its own rules is illogical. You can put words and phrases in front of main clauses that modify the 'subject' of the clause rather than the verb ie they're 'adjectival'.