core-bundle/src/Resources/contao/library/Contao/Model/Registry.php
public function isRegisteredAlias(Model $objModel, $strAlias, $varValue)
	{
		$strTable = $objModel->getTable();

		return isset($this->arrAliases[$strTable][$strAlias][$varValue]);
	}
public function isRegisteredAlias(Model $objModel, $strAlias, $varValue)
	{
		$strTable = $objModel->getTable();

		return isset($this->arrAliases[$strTable][$strAlias][$varValue]);
	}
Check if an alias is registered

@param Model  $objModel The model object
@param string $strAlias The alias name
@param mixed  $varValue The value of the alias

@return boolean True if the alias is registered