ID

• Value must be an XML name

  • May include letters, digits, underscores, hyphens, and periods

  • May not include whitespace

  • May or may not have the name "id" or "ID"

  • May contain colons only if used for namespaces

• Value must be unique within ID type attributes in the document

• Generally the default value is #REQUIRED

<!ELEMENT composer (name)>
<!ATTLIST composer id ID #REQUIRED>