[css-values] Define a top-level list

[cdoublev]

Comma-ellision rules are defined in CSS Values as applicable within a top-level list in a property or other CSS value, or a function’s argument list.

What defines a top-level list? Does the following definition value (from CSS Images 3) contain a "sub-level" list? Are [] (grouping) the only way to define a sub-level list?

<linear-color-stop> , [ <linear-color-hint>? , <linear-color-stop> ]#

The spec defines that a comma is implicitly omissible in some circumstances, when used to separate optional terms.

Side note: imo, I think it should be [...] to separate an optional term.

In the above definition, the second comma can be omitted only if [ <linear-color-hint>? , <linear-color-stop> ] defines a top-level list and all items preceding the comma have been omitted. If it does not define a top-level list and it is a sub-level list, then the second comma can not be omitted.

Defining a top-level list would make things more clear, at least for me, I think. I can't find any other "top-level list" occurrences in CSS Values.

[tabatkins]

"top-level" meaning "not nested into a block or function". It doesn't have anything to do with the grammar itself, but rather the CSS constructs in the value.

We use the term "top-level" in other contexts, like in Variables to refer to top-level ! values.

[cdoublev]

I was wrong in my initial comment: CSS Values does include a second occurrence of "top-level list" in such a type [bearing a property name between quotes] does not include [...] any top-level comma-separated-list multiplier. I guess my confusion is there, and the meaning of "top-level" is obvious. Thank you tabatkins.