This function returns 1 (true) if the tag named tagname is declared as a link element in the .dcf file for the document type associated with doc. If doc is omitted or 0, the current document is used.
Remarque :
If you have applied an alias map to the document, tagname can be either an alias or a real name.
Remarque :
If the document type definition for your document instance includes the NAMECASE GENERAL NO setting, then the tagname parameter will be case-sensitive.