This uses syntax from https://phpstan.org/writing-php-code/phpdoc-types#general-arrays.
int[] means an array of ints with arbitrary keys (usually strings)
list<string> means an array of strings with sequential integer keys starting at 0
list<string>[] means an arbitrary array of string lists
list<string[]> means list of arbitrary string arrays
string[][] means two dimensional array with arbitrary keys in both dimensions
array was left in the comments for https://phpstan.org/writing-php-code/phpdoc-types#array-shapes
