The difference between PHP merge array array_merge function operator plus sign and - PHP tutorial

The description of array_merge in the reference manual is as follows:
array_merge() Merges the cells of two or more arrays, and the values ​​in one array are appended to the previous array. Returns the resulting array.
If there is the same string key name in the input array, the value after the key name will overwrite the previous value. However, if the array contains numeric keys, the subsequent values ​​will not overwrite the original values ​​but will be appended to them.
The difference between the two is:
1. When the array key name is a numeric key name, and the two arrays to be merged have numeric KEYs with the same name, using array_merge() will not overwrite the original value. Using "+" to merge arrays will return the first appearing value as the final result, and "discard" those values ​​with the same key name in subsequent arrays (note: not overwriting but retaining the first appearing value) . Example:

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