This function returns a new instance of class DOMComment. The content of the comment is the value of the passed 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 DOMNode->appendChild(), DOMDocument->createElement(), DOMDocument->createTextNode(), DOMDocument->createAttribute(), DOMDocument->createProcessingInstruction().