This function returns the namespace URI prefixed to the primary element for the given style specified in the document type configuration file (.dcf) for the document type associated with doc. Valid style values are bold, italic, and underline.

If a tag name is returned, text_style_tag_name_ns function returns arr.

The function returns the null string if there isn’t a namespace prefix, if no element is defined for the specified style, or if doc is invalid or an ASCII file. If doc is omitted or 0, the current document is used.