Adds a new attribute. If an attribute with that name is already present
in the element, its value is changed to be that of the value
parameter. This value is a simple string; it is not parsed as it is
being set. So any markup (such as syntax to be recognized as an
entity reference) is treated as literal text, and needs to be
appropriately escaped by the implementation when it is written out.
In order to assign an attribute value that contains entity
references, the user must create an
Attr node plus any
EntityReference nodes, build the
appropriate subtree, and use
setAttributeNode to assign
it as the value of an attribute.
To set an attribute with a qualified name and namespace URI, use the
|The name of the attribute to create or alter.|
|Value to set in string form.|
| INVALID_CHARACTER_ERR: Raised if the specified name is not an XML
name according to the XML version in use specified in the
NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.