$array
=
[
0 => 0,
1 => 'color',
]
#1
|
array_keys
|
([0 => 100, "color" => "red"])
|
#2
|
array_keys
|
([0 => "blue", 1 => "red", 2 => "green", 3 => "blue", 4 => "blue"], |
#3
|
array_keys
|
(["color" => [0 => "blue", 1 => "red", 2 => "green"], "size" => [0 => "small", 1 => "medium", 2 => "large"]])
|