probleme validation

in the file status.php of the wall I have this to validate the message
$ footer. = elgg_view_field ([
'#type' => 'fieldset',
'align' => 'horizontal',
'justify' => 'right', // button and selection Post valdation of the wall message
'fields' => [
[
'#type' => 'access',
'name' => 'access_id',
'value' => $ entity? $ entity-> access_id: get_default_access (),
'class' => 'wall-access',
]
[
'#type' => 'submit',
'value' => elgg_echo ('wall: post'),
]
]
]);

the submit type button reboots to Post;

I would like to know where I can find the Post code.

I look in the file post.php but it is not there that I am redirected

can you help me thanks