src/includes/classes/Core/Utils/RequestType.php
public function doingRestAction(string $action = null): string
    {
        if (isset($action)) {
            $this->doing_rest_action = $action;
            $this->doingAction($action, true);
        }
        return (string) $this->doing_rest_action;
    }
public function doingRestAction(string $action = null): string
    {
        if (isset($action)) {
            $this->doing_rest_action = $action;
            $this->doingAction($action, true);
        }
        return (string) $this->doing_rest_action;
    }
Doing a REsT action?

@since 160531 Request types.

@param string|null $action Only to set action.

@return string The REsT action being done.