wp-includes/general-template.php:2864Outputs the date in iso8601 format for xml files.
function the_date_xml() { echo mysql2date( 'Y-m-d', get_post()->post_date, false );}Introduced in 1.0.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/general-template.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.