This function determines if the given document is case sensitive when dealing with markup. The function returns a one (1) or zero (0) based on the NAMECASE GENERAL setting of the document type definition (DTD) associated with the optional document ID parameter doc. If doc is omitted, the current document is used. A return of zero (0) means case-insensitive (that is, NAMECASE GENERAL YES). A return of one (1) means case-sensitive (that is, NAMECASE GENERAL NO). This function always returns one (1), if doc is an XML document, because XML markup is always case-sensitive.