(glib:define-gboxed-opaque paper-size "GtkPaperSize"
  :export t
  :type-initializer "gtk_paper_size_get_type"
  :alloc (%paper-size-alloc (cffi:null-pointer)))  

The gtk:paper-size instance handles paper sizes. The gtk:paper-size structure is opaque, and has no user visible fields. It uses the standard called "PWG 5101.1-2002 PWG: Standard for Media Standardized Names" to name the paper sizes and to get the data for the page sizes. In addition to standard paper sizes, the gtk:paper-size structure allows to construct custom paper sizes with arbitrary dimensions.

The gtk:paper-size structure stores not only the dimensions (width and height) of a paper size and its name, it also provides default print margins.