Square brackets in HTML form arrays. Just conventional or with a meaning?

Question

I frequently see, in particular in the PHP world, the following writing if you want to create a FORM array.

Answer 1

It's just conventional.

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The W3C states:

Let the form data set be a list of name-value-type tuples

and for each input element, on submit:

Append an entry to the form data set with name as the name, the value of the field element as the value, and type as the type.

The W3C does not mention the use of [] or uniqueness of the name attribute.