12. A method for rendering a page description language (PDL) document, the method comprising: receiving identifying metadata for a first occurrence of a sequence of reusable objects identified in a first display list, a reusable intermediate graphical representation for the sequence of reusable objects being cached for further reuse in a format intermediate between a display list and pixel data; identifying a second occurrence of the sequence of reusable objects in the PDL document using the received identifying metadata, the identified second occurrence being associated with a z-order position in the PDL document of the second occurrence; grouping objects of the PDL document into a plurality of z-bands, the plurality of z-bands including a reusable z-band for the identified second occurrence and a further z-band based on the z-order position of the second occurrence; generating a display list representation for the PDL document, by creating a reference to the cached reusable intermediate graphical representation for the reusable z-band at the z-order position of the identified second occurrence; and generating an intermediate graphical representation to render the PDL document, the intermediate graphical representation being generated by merging the reusable intermediate graphical representation with an intermediate representation for the further z-band using the generated display list representation.
12. A method for rendering a page description language (PDL) document, the method comprising: receiving identifying metadata for a first occurrence of a sequence of reusable objects identified in a first display list, a reusable intermediate graphical representation for the sequence of reusable objects being cached for further reuse in a format intermediate between a display list and pixel data; identifying a second occurrence of the sequence of reusable objects in the PDL document using the received identifying metadata, the identified second occurrence being associated with a z-order position in the PDL document of the second occurrence; grouping objects of the PDL document into a plurality of z-bands, the plurality of z-bands including a reusable z-band for the identified second occurrence and a further z-band based on the z-order position of the second occurrence; generating a display list representation for the PDL document, by creating a reference to the cached reusable intermediate graphical representation for the reusable z-band at the z-order position of the identified second occurrence; and generating an intermediate graphical representation to render the PDL document, the intermediate graphical representation being generated by merging the reusable intermediate graphical representation with an intermediate representation for the further z-band using the generated display list representation. 14. The method according to claim 12 , wherein image data for display list objects is associated with unique identifiers.