and add an array array_merge

array_merge()

Indexed array: values are not covered, it will be re-indexed; 
associative arrays: the same keys, the last element will cover other elements.

 

Array +

The left main, plus key;
 the Array 
( 
    [ 0] => A006 
)
 +
 the Array 
( 
    [ 0] => A004 
    [ . 1] => A006 
)
 =
 the Array 
( 
    [ 0] => A006 
    [ . 1] => A006 
)