WordPress at a glance
function is not described

_wp_get_allowed_postdata() WP 4.9.9

Returns only allowed post data fields

No Hooks.

Return

Object/true/false. WP_Error on failure, true on success.

Usage

_wp_get_allowed_postdata( $post_data );
$post_data(array)
Array of post data.
Default: contents of $_POST

Code of wp get allowed postdata: wp-admin/includes/post.php VER 5.0.3

<?php
function _wp_get_allowed_postdata( $post_data = null ) {
	if ( empty( $post_data ) ) {
		$post_data = $_POST;
	}

	// Pass through errors
	if ( is_wp_error( $post_data ) ) {
		return $post_data;
	}

	return array_diff_key( $post_data, array_flip( array( 'meta_input', 'file', 'guid' ) ) );
}