wp-includes/class-wp-customize-control.php:706An Underscore (JS) template for this control's content (but not its container).
protected function content_template() {}Introduced in 4.1.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-control.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.