How does this array value the key value?

How does this array value the key value???
[Country/region:] = = Array
(
[0] = Mainland China
)

I want to value the key value??

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Not necessarily
Key ($array)
------Solution--------------------
I'm sorry. That's the opposite.
The current () function can return the cell of the array, and the default is the first one
Key () takes the value of the current cell.
http://www.php.net/manual/zh/function.current.php
------Solution--------------------
Array_keys

Iterating over the obtained array of key values

Key with current must first reset
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Unfortunately, you have only one key and one subscript.
[' [Country/region: '][0]
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What's the value of a key?

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