What postscript object is 8-bytes normally, but 9-bytes packed?

A packed array in Postscript is supposed to be a space-saving feature, where objects can be squeezed tightly in memory by omitting extraneous information. Like a null can be just a single byte because it carries no information. Booleans could be a signel byte, too. Integers could be 5 (or 3) bytes (if it's a small number). Reference objects would need the ful开发者_开发问答l 8-bytes that a normal object does. But the Postscript Manual says that packed objects occupy 1-9 bytes!

When the PostScript language scanner encounters a procedure delimited by { … }, it creates either an array or a packed array, according to the current packing mode (see the description of the setpacking operator in Chapter 8). An array value occupies 8 bytes per element. A packed array value occupies 1 to 9 bytes per element, depending on each element’s type and value; a typical average is 2.5 bytes per element. --PLRM 3ed, B.2. Virtual Memory Use, p. 742

So what object gets bigger when packed? And Why? Hydrogen-bonding??!

Any value that you can't represent in 7 bytes or less, will need 9 bytes.

The packed format starts with a byte that contains how many data bytes follow, so any value that needs all 8 bytes of data will be 9 bytes including the leading length byte.