How does the Installer handle the «setup_version» attribute for a module?

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1

setup/src/Magento/Setup/Model/Installer.php#L820-L857

foreach ($moduleNames as $moduleName) {
	$this->log->log("Module '{$moduleName}':");
	$configVer = $this->moduleList->getOne($moduleName)['setup_version'];
	$currentVersion = $moduleContextList[$moduleName]->getVersion();
	// Schema/Data is installed
	if ($currentVersion !== '') {
		$status = version_compare($configVer, $currentVersion);
		if ($status == \Magento\Framework\Setup\ModuleDataSetupInterface::VERSION_COMPARE_GREATER) {
			$upgrader = $this->getSchemaDataHandler($moduleName, $upgradeType);
			if ($upgrader) {
				$this->log->logInline("Upgrading $type.. ");
				$upgrader->upgrade($setup, $moduleContextList[$moduleName]);
			}
			if ($type === 'schema') {
				$resource->setDbVersion($moduleName, $configVer);
			} elseif ($type === 'data') {
				$resource->setDataVersion($moduleName, $configVer);
			}
		}
	} elseif ($configVer) {
		$installer = $this->getSchemaDataHandler($moduleName, $installType);
		if ($installer) {
			$this->log->logInline("Installing $type... ");
			$installer->install($setup, $moduleContextList[$moduleName]);
		}
		$upgrader = $this->getSchemaDataHandler($moduleName, $upgradeType);
		if ($upgrader) {
			$this->log->logInline("Upgrading $type... ");
			$upgrader->upgrade($setup, $moduleContextList[$moduleName]);
		}
		if ($type === 'schema') {
			$resource->setDbVersion($moduleName, $configVer);
		} elseif ($type === 'data') {
			$resource->setDataVersion($moduleName, $configVer);
		}
	}
	$this->logProgress();
}