Like custom stream handlers, custom chunk handlers are implemented using
Release 2 Hook structures.  See the previous section for details on how a
handler function may be interfaced using a Hook structure.

There are two types of chunk handlers:  entry handlers and exit handlers.
Entry handlers are invoked just after the parser enters the chunk; the
stream will be positioned to read the first byte in the chunk. (If the
chunk is a FORM, LIST, CAT, or PROP, the longword type will be read by the
parser; the stream will be positioned to read the byte immediately
following the type.)  Exit handlers are invoked just before the parser
leaves the chunk; the stream is not positioned predictably within the
chunk.

 Installing a Custom Chunk Handler 
 Inside a Custom Chunk Handler 
 The Object Parameter