cairo:pdf-surface-set-custom-metadata (surface name value)

surface -- a cairo:surface-t instance
name -- a string for the name of the custom metadata item to set (UTF8)
value -- a string for the value of the metadata (UTF8)

Set custom document metadata. The name argument may be any string except for the following names reserved by PDF: "Title", "Author", "Subject", "Keywords", "Creator", "Producer", "CreationDate", "ModDate", "Trapped".

If the value argument is nil or an empty string, the name metadata will not be set.

(cairo:pdf-surface-set-custom-metadata surface "ISBN" "978-0123456789")    

Since 1.18