`ValueWithShadows()` called in function `newMarkupSanitizer()` (file `modules/setting/markup.go`) always returns one element. For example, the following section in `app.ini` means "rel" attribute is allowed for "a" element while "target" attribute is still ignored. ``` [markup.sanitizer] ELEMENT = a ALLOW_ATTR = target REGEXP = ELEMENT = a ALLOW_ATTR = rel REGEXP = ```