Set the custom title for the top level category '{$a->name}' with id '{$a->id}' and its children '{$a->children}' in the header.  If blank then you will be presented with what has been configured by the 'sitetitle' and 'sitetitletext' settings on non-course pages or on course pages when 'enableheading' is 'off'.  When populated on non-course category linked pages then this will replace the site title.  When populated on course pages then will appear above the title as established by the 'enableheading' setting.  But on mobiles any 'title' will only appear depending on the 'responsivecoursetitle' setting.