Sample-LGR-Thaana.xml

<?xml version="1.0" encoding="utf-8"?>
<lgr xmlns="http://www.iana.org/lgr/0.1">
  <meta>
    <version comment="Sample LGR for Thaana">1</version>
    <date>2014-11-29</date>
    <language>und-Thaa</language>
    <scope type="domain">.</scope>
    <unicode-version>6.3.0</unicode-version>
    <description type="text/html"><![CDATA[
        <h1>Label Generation Rules for Thaana: Sample LGR for Thaana</h1>
        <h2>Overview</h2>
        <p>This file contains a sample of a possible set of Label Generation Rules for Thaana
        using a limited repertoire as would be appropriate for the Root Zone.</p> 
        
        <p>Unicode encodes consonants and vowels separately for Thaana, even though, in practice,
        all consonants must be followed by a vowel, with the single exception of U+0782. These restrictions
        are implemented by context rules (when rules) attached to each code point, except U+0782.</p>
        
        <p>There are further constraints on the allowable contexts for U+0782 when not followed by a vowel,
        but trying to enforce those yields diminishing returns.</p>
        
        <h2>Repertoire</h2>
        <p>The sample repertoire does not contain digits. For zones that allow digits, an appropriate set of
         digits would have to be added. (All code points are tagged as either vowels or consonants.) The "ref"   
         attribute for each code point or range contains the Unicode version for which the corresponding
        code points were first encoded (for example, ref="3" means a character was first encoded in Unicode 
        Version 3.0).
        </p>
        
        <p>The "tag" attribute for each code point or range also indicates the script or scripts that the code
         point is used with, using Unicode script identifiers preceded by "sc:".</p>
        
        <h2>Thaana-specific Rules</h2>
        
        <p>There are two context rules specific to Thaana ("precedes-vowel" and "follows-consonant"). They are
        implemented as context rules (when rules), so no corresponding action element needs to be defined.</p>
        
        <h2>Default Whole Label Evaluation Rules</h2>
        
        <p>The sample LGR includes the default WLE rules as well as the actions that would be applicable by
        default for the Root Zone. For other zones, other applicable rules may be included. In this sample,
        the "leading-combining-mark" rule is never expected to be matched, because the only combining marks
        are vowels and they cannot occur except after a consonant by application of the "follows-consonant"
        context rule.</p>
        ]]></description>
    <references>
      <reference id="3">The Unicode Standard 3.0</reference>
      <reference id="5">The Unicode Standard 3.2</reference>
    </references>
  </meta>
  <data>
    <range first-cp="0780" last-cp="0781" tag="sc:Thaa consonant" ref="3" when="precedes-vowel" />
    <char cp="0782" tag="sc:Thaa consonant" ref="3" />
    <range first-cp="0783" last-cp="07A5" tag="sc:Thaa consonant" ref="3" when="precedes-vowel" />
    <range first-cp="07A6" last-cp="07B0" tag="sc:Thaa vowel" ref="3" when="follows-consonant" />
    <char cp="07B1" tag="sc:Thaa consonant" ref="5" when="precedes-vowel" />
  </data>
  <!--Rules section goes here-->
  <rules>
    <!--Character class definitions go here-->
    <!--Whole label evaluation and context rules go here-->
    <rule name="leading-combining-mark" comment="Default WLE rule">
      <start />
      <union>
        <class property="gc:Mn" />
        <class property="gc:Mc" />
      </union>
    </rule>
    <rule name="follows-consonant">
      <look-behind>
        <class from-tag="consonant" />
      </look-behind>
      <anchor />
    </rule>
    <rule name="precedes-vowel">
      <anchor />
      <look-ahead>
        <class from-tag="vowel" />
     </look-ahead>
   </rule>

    <!--Action elements go here - order defines precedence-->
    <action disp="invalid" match="leading-combining-mark" />
    <action disp="invalid" any-variant="out-of-repertoire-var" comment="any variant label with a code point out of repertoire is invalid" />
    <action disp="blocked" any-variant="blocked" />
    <action disp="allocatable" any-variant="allocatable" />
    <action disp="valid" comment="catch all" />
  </rules>
</lgr>