<attDef>

<attDef> (attribute definition) contains the definition of a single attribute. 22.4.5 Attribute List Specification
Module tagdocs — 22 Documentation Elements
In addition to global attributes att.identified (@ident, @predeclare, @module, @mode)
usage specifies the optionality of an attribute or element.
Status Optional
Legal values are:
req
(required)
mwa
(mandatory when applicable )
rec
(recommended )
rwa
(recommended when applicable )
opt
(optional ) [Default]
ns (namespace) specifies the namespace to which this attribute belongs
Status Optional
Datatype 

<rng:ref name="data.namespace"/>
data.namespace
Used by
attList
May contain
certainty: certainty precision respons
core: desc gloss
tagdocs: altIdent constraintSpec datatype defaultVal equiv exemplum remarks valDesc valList
Declaration 

<rng:element name="attDef">
 <rng:ref name="att.global.attributes"/>
 <rng:ref name="att.identified.attributes"/>
 <rng:optional>
  <rng:attribute name="usage" a:defaultValue="opt">
   <rng:choice>
    <rng:value>req</rng:value>
    <rng:value>mwa</rng:value>
    <rng:value>rec</rng:value>
    <rng:value>rwa</rng:value>
    <rng:value>opt</rng:value>
   </rng:choice>
  </rng:attribute>
 </rng:optional>
 <rng:optional>
  <rng:attribute name="ns"
    a:defaultValue="http://www.tei-c.org/ns/1.0">
   <rng:ref name="data.namespace"/>
  </rng:attribute>
 </rng:optional>
 <rng:group>
  <rng:zeroOrMore>
   <rng:ref name="model.glossLike"/>
  </rng:zeroOrMore>
  <rng:optional>
   <rng:ref name="datatype"/>
  </rng:optional>
  <rng:zeroOrMore>
   <rng:ref name="constraintSpec"/>
  </rng:zeroOrMore>
  <rng:optional>
   <rng:ref name="defaultVal"/>
  </rng:optional>
  <rng:optional>
   <rng:choice>
    <rng:ref name="valList"/>
    <rng:oneOrMore>
     <rng:ref name="valDesc"/>
    </rng:oneOrMore>
   </rng:choice>
  </rng:optional>
  <rng:zeroOrMore>
   <rng:ref name="exemplum"/>
  </rng:zeroOrMore>
  <rng:zeroOrMore>
   <rng:ref name="remarks"/>
  </rng:zeroOrMore>
 </rng:group>
</rng:element>
element attDef
{
   att.global.attributes,
   att.identified.attributes,
   attribute usage { "req" | "mwa" | "rec" | "rwa" | "opt" }?,
   attribute ns { data.namespace }?,
   (
      model.glossLike*,
      datatype?,
      constraintSpec*,
      defaultVal?,
      ( valList | valDesc+ )?,
      exemplum*,
      remarks*
   )
}
Example
<attDef usage="rec" ident="type">
 <desc>specifies a name conventionally used for this level of subdivision, e.g.
 <val>act</val>, <val>volume</val>, <val>book</val>, <val>section</val>, <val>canto</val>,
   etc.</desc>
</attDef>