Valid_exit_codes understanding

Given the following example,

“pause_before”: “10s”,
“type”: “powershell”,
“inline”: [
“do something and raise return code x”,
“do something and raise return code y”,
“do something and raise return code z”
],
“valid_exit_codes”: [
0
]

Does Packer only look at last line of inline block to determine the exit code or does it look at the highest of the list or what?