This function returns the real name as specified in the DTD of the specified attribute value, where value is the real name or alias of the attribute value. Specify attr and element if you want this function to return the real name of an element-specific attribute value (element and attr can be real names or aliases). If both attr and element are omitted, this function returns the real name of a global attribute value.

The doc argument specifies the identifier of the document tree to query. If omitted or 0, the current document is searched.