documentation synopsis grammar

Hallo

I search for it and did notsucceeded.
Where is exact definition of the grammar used here?

I thing the text "[,...]" is unclear concerning what is to be repeted.

here:
*https://www.postgresql.org/docs/9.6/static/notation.html
<https://www.postgresql.org/docs/9.6/static/notation.html>*
you state
*" Dots (...) mean that the preceding element can be repeated. "*

from that definition the fragment "[,...]" means zero or more commas.

It is often so that not one element but several elements are repeated .

Sometimes from the context, one may find out how it is meant.
In other cases it not so clear .

Well do you have a definition or third party standard?

Thank you very much,Peter Korim.