core-bundle/src/Resources/contao/classes/BackendTemplate.php
public function parse()
	{
		$strBuffer = parent::parse();

		// HOOK: add custom parse filters
		if (isset($GLOBALS['TL_HOOKS']['parseBackendTemplate']) && \is_array($GLOBALS['TL_HOOKS']['parseBackendTemplate']))
		{
			foreach ($GLOBALS['TL_HOOKS']['parseBackendTemplate'] as $callback)
			{
				$this->import($callback[0]);
				$strBuffer = $this->{$callback[0]}->{$callback[1]}($strBuffer, $this->strTemplate);
			}
		}

		return $strBuffer;
	}
public function parse()
	{
		$strBuffer = parent::parse();

		// HOOK: add custom parse filters
		if (isset($GLOBALS['TL_HOOKS']['parseBackendTemplate']) && \is_array($GLOBALS['TL_HOOKS']['parseBackendTemplate']))
		{
			foreach ($GLOBALS['TL_HOOKS']['parseBackendTemplate'] as $callback)
			{
				$this->import($callback[0]);
				$strBuffer = $this->{$callback[0]}->{$callback[1]}($strBuffer, $this->strTemplate);
			}
		}

		return $strBuffer;
	}
Add a hook to modify the template output

@return string