Set custom document metadata. name may be any string except for
the following names reserved by PDF: "Title", "Author", "Subject",
"Keywords", "Creator", "Producer", "CreationDate", "ModDate",
"Trapped".
If value is NULL or an empty string, the name metadata will not be set.
For example:
<informalexample><programlisting>
cairo_pdf_surface_set_custom_metadata (surface, "ISBN", "978-0123456789");
</programlisting></informalexample>
Set custom document metadata. name may be any string except for the following names reserved by PDF: "Title", "Author", "Subject", "Keywords", "Creator", "Producer", "CreationDate", "ModDate", "Trapped".
If value is NULL or an empty string, the name metadata will not be set.
For example: <informalexample><programlisting> cairo_pdf_surface_set_custom_metadata (surface, "ISBN", "978-0123456789"); </programlisting></informalexample>