This function returns a new instance of class
DomAttribute. The name of the attribute is the
value of the first parameter. The value of the attribute is the value of
the second parameter. 本节点不会出现在文档中，除非是用例如
domnode_append_child() 函数来将其插入。
The return value is FALSE if an error occurred.
See also domnode_append_child(), domdocument_create_element(), domdocument_create_text(), domdocument_create_cdata_section(), domdocument_create_processing_instruction(), domdocument_create_entity_reference(), and domnode_insert_before().