This function returns a new instance of class DOMAttr. The name of the attribute is the value of the first parameter. 本节点不会出现在文档中，除非是用例如 DOMNode->appendChild() 来插入的。
The return value is FALSE if an error occurred.
See also DOMDocument->createElement(), DOMNode->appendChild(), DOMDocument->createTextNode(), DOMDocument->createComment() and DOMDocument->createProcessingInstruction().