Grammatica - loco

3
Punctuation
22
The following subtle difference in meaning when the first comma is omitted
or used should be noted: with a comma the relative clause relates back to
the entire group, whereas without a comma it refers to only a section of
the group; strictly speaking this is the same in English (called non-restrictive
and restrictive relative clauses respectively) although many people are
unaware of the distinction:
De jongens, die te laat waren, moesten schoolblijven.
The boys, who were late, had to stay behind at school.
(i.e. There were only boys and all had to stay behind.)
De jongens die te laat waren, moesten schoolblijven.
The boys who were late had to stay behind at school.
(i.e. There were other boys and perhaps girls who were not late.)
3.1.4
Note that the following English commas, which merely indicate a reading
pause within a clause, are not used in Dutch:
Het is echter erg moeilijk.
It is, however, very difficult.
Hij heeft het helaas niet gedaan/Helaas heeft hij het niet
gedaan.
He has, unfortunately, not done it/Unfortunately, he hasn’t done it.
3.1.5
See 14.1.1.2 and 14.7 for use of the comma with numerals.