wp-includes/deprecated.php:3448Formerly used to escape strings before inserting into the DB.
$contentstringstringfunction format_to_post( $content ) { _deprecated_function( __FUNCTION__, '3.9.0' ); return $content;}Introduced in 0.71. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/deprecated.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.