| − | * single quoted strings don't recognize special character codes like \n <ref name="sitepoint">[http://www.sitepoint.com/article/advanced-email-php/3/ Advanced PHP from Sitepoint]</ref> | + | * single quoted strings don't recognize most special character codes like \n <ref name="sitepoint">[http://www.sitepoint.com/article/advanced-email-php/3/ Advanced PHP from Sitepoint]</ref> and don't expand variables, however they do recognize \' and \\ |