code: public function getLayoutSections()
  	{
  		$arrSections = array('header', 'left', 'right', 'main', 'footer');
  
  		// Check for custom layout sections
  		$objLayout = $this->Database->query("SELECT sections FROM tl_layout WHERE sections!=''");
  
  		while ($objLayout->next())
  		{
  			$arrCustom = Contao\StringUtil::deserialize($objLayout->sections);
  
  			// Add the custom layout sections
  			if (!empty($arrCustom) && \is_array($arrCustom))
  			{
  				foreach ($arrCustom as $v)
  				{
  					if (!empty($v['id']))
  					{
  						$arrSections[] = $v['id'];
  					}
  				}
  			}
  		}
  
  		return Contao\Backend::convertLayoutSectionIdsToAssociativeArray($arrSections);
  	}
docs: Return all layout sections as array
  
  @return array