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apply_filters( 'pingback_useragent', string $concat_useragent, string $useragent, string $pingback_server_url, string $pagelinkedto, string $pagelinkedfrom )

Filters the user agent sent when pinging-back a URL.

$concat_useragent: (string) The user agent concatenated with ' -- WordPress/' and the WordPress version.
$useragent: (string) The useragent.
$pingback_server_url: (string) The server URL being linked to.
$pagelinkedto: (string) URL of page linked to.
$pagelinkedfrom: (string) URL of page linked from.

Used By	Description
wp-includes/comment.php: pingback()	Pings back the links found in a post.

Version	Description
2.9.0	Introduced.

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Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/hooks/pingback_useragent