Proposal for @selector attribute on rendition

This proposal arises out of FR 520, which presents a number of ideas for enhancements to the <rendition> element. This proposal is the simplest and most straightforward, consisting of a single new attribute, which I believe will be the least controversial and easiest to implement.

Rationale

The combination of <rendition> and @rendition currently allows us to link specific elements with blocks of style code (almost always CSS) in the manner of the HTML @class attribute, and @style allows the direct application of CSS to a specific element. What we cannot currently do is specify a default rendition for an element or a set of elements, except through the use of <tagUsage>/@render; this is crude in allowing only the linking of style blocks with unqualified elements, and it also brings in the requirement that every element used be provided with a matching <tagUsage> element.

I would argue that a better approach would be a new attribute called @selector available on the <rendition> element, through the att.styleDef class. Its definition would be:

A selector or series of selectors specifying the elements to which the contained style description applies, expressed in the language specified in the @scheme attribute.

This would allow simple definitions like the following:

  <rendition 
     scheme="css" 
     selector="text front back body div p ab">
     display: block;
  </rendition>

making this a straighforward way in which to express a basic mapping between TEI elements and their default styles. It would of course allow much more sophisticated mapping, including for instance the use of @rend:

  <rendition 
     scheme="css" 
     selector="*[rend*=italic]">
     font-style: italic;
  </rendition>

and would make it easy to express different default rules for the same element in different contexts:

  <rendition 
     scheme="css" 
     selector="front p, back p">
     margin-top: 0.5em;
  </rendition>

  <rendition 
     scheme="css" 
     selector="body p">
     margin-top: 0;
  </rendition>

Details

ODD

This is the proposed ODD fragment, to be added to att.styleDef.xml:

  <attDef ident="selector">
     <desc versionDate="2015-05-25" xml:lang="en">
        A selector or series of selectors specifying the elements to which the contained style 
        description applies, expressed in the language specified in the <att>scheme</att> attribute.
     </desc>
     <datatype maxOccurs="1">
       <ref xmlns="http://relaxng.org/ns/structure/1.0" name="data.text"/>
     </datatype>
     <exemplum xml:lang="en">
        <egXML xmlns="http://www.tei-c.org/ns/Examples">
           <rendition 
              scheme="css" 
              selector="text front back body div p ab">
              display: block;
           </rendition>
        </egXML>
     </exemplum>
     <exemplum xml:lang="en">
        <egXML xmlns="http://www.tei-c.org/ns/Examples">
           <rendition 
              scheme="css" 
              selector="*[rend*=italic]">
              font-style: italic;
           </rendition>
        </egXML>
     </exemplum>
     <remarks versionDate="2015-05-25" xml:lang="en">
        Since the default value of the <att>scheme</att> attribute is assumed to be CSS, the default 
        expectation for this attribute, in the absence of <att>scheme</att>, is that CSS selector
        syntax will be used.
     </remarks>
     <remarks versionDate="2015-05-25" xml:lang="en">
        While <att>rendition</att> is used to point from an element in the transcribed source to a 
        <gi>rendition</gi> element in the header which describes how it appears, the <att>selector</att>
        attribute allows the encoder to point in the other direction: from a <gi>rendition</gi> in the
        header to a collection of elements which all share the same renditional features. In both cases,
        the intention is to record the appearance of the source text, not to prescribe any particular 
        output rendering.
     </remarks>
  </attDef>

Chapter prose

These are proposed changes to the prose of Chapter 2:

2.3.4 The Tagging Declaration

One or more such specifications may be associated with elements of a document in two three ways:

• the @render attribute of the appropriate tagUsage element may be used to indicate a default rendition for all occurrences of the named element
• the @selector attribute on any <rendition> element may be used to select a collection of elements to which it applies
• the global @rendition attribute may be used on any element to indicate its rendition, overriding or complementing any supplied default value