Programmer's Guide > Interfaces > W3C Attr interface > isId attribute
  
isId attribute
Returns whether this attribute is known to be of type ID (i.e. to contain an identifier for its owner element) or not. When it is and its value is unique, the ownerElement of this attribute can be retrieved using the method Document.getElementById. The implementation could use several ways to determine if an attribute node is known to contain an identifier:
If validation occurred using an XML Schema [XML Schema Part 1] while loading the document or while invoking Document.normalizeDocument(), the post-schema-validation infoset contributions (PSVI contributions) values are used to determine if this attribute is a schema-determined ID attribute using the schema-determined ID definition in [XPointer].
If validation occurred using a DTD while loading the document or while invoking Document.normalizeDocument(), the infoset [type definition] value is used to determine if this attribute is a DTD-determined ID attribute using the DTD-determined ID definition in [XPointer].
from the use of the methods Element.setIdAttribute(), Element.setIdAttributeNS(), or Element.setIdAttributeNode(), i.e. it is an user-determined ID attribute;
* 
XPointer framework (see section 3.2 in [XPointer]) consider the DOM user-determined ID attribute as being part of the XPointer externally-determined ID definition.
using mechanisms that are outside the scope of this specification, it is then an externally-determined ID attribute . This includes using schema languages different from XML schema and DTD.
If validation occurred while invoking Document.normalizeDocument(), all user-determined ID attributes are reset and all attribute nodes ID information are then reevaluated in accordance to the schema used. As a consequence, if the Attr.schemaTypeInfo attribute contains an ID type, isId will always return true.
isId
Access
read-only
Returns
boolean