[Guy Harris <guy@xxxxxxxxxxxx>]

Douglas Pratley wrote:

> b) Adds functionality analogous to dissector tables, but instead of 
> directing by field values, there is a list of display-filter / 
> sub-dissector pairs. A sub-dissector is called if the display filter is 
> matched by the packet.

Display filter values are available only if a protocol tree is being 
constructed.

This means that, if this mechanism is enabled, you have to force the 
construction of a protocol tree; presumably, if it's *not* enabled, 
construction of a protocol tree is *not* forced (forcing the 
construction of a protocol tree if the protocol tree won't be used 
imposes a significant performance cost).