Question about normative language re processors and the new <sort-as> element

Currently, the spec draft basically says that processors SHOULD
    handle the <sort-as> element in certain ways. (Text copied
    below)

    

    A review comment asks why this is not a MUST statement.

    

    -----------------

    

    
Processors SHOULD
      expect to encounter <sort-as>
      elements in the above locations and process them correctly,
      including the following considerations and precedence rules:

    
      
A <sort-as>
        element that is specified in a title takes precedence over a <sort-as> element that is
        specified in the topic prolog. 

      
Except for instances in the topic prolog,
        processors should only apply <sort-as>
        elements that are either a direct child of the element to be
        sorted or a direct child of the title- or label-defining element
        of the element to be sorted. 

      
When an element contains multiple, direct-child, <sort-as> elements, the first
        direct-child <sort-as>
        element in document order takes precedence. Within topic
        prologs, the first <sort-as>
        element in document order takes precedence. 

      
When located within an
          <indexterm> element, the <sort-as> element is
        equivalent to <index-sort-as>.
        It is an error for an <indexterm>
        element to directly contain both <sort-as>
        and <index-sort-as>
        elements. 

      
Sort phrases are determined after filtering and
        content reference resolution is applied. 

    
    
When a <sort-as>
      element is specified, processors that sort the containing element
      MUST construct the effective sort
      phrase by prepending the content of the <sort-as>
      element to the base sort phrase. This ensures that two items with
      the same <sort-as> element
      but different base sort phrases will sort in the appropriate
      order.

    

    
-- 

      Best,

      Kris

      

      Kristen James Eberlein

      Chair, OASIS DITA Technical Committee

      Principal consultant, Eberlein Consulting

      www.eberleinconsulting.com

      +1 919 682-2290; kriseberlein (skype)