[sv-ec] Semantics of anonymous_program

Hi,
In SV3.1a LRM at BNF section A.1.10 there is a reference of
anonymous_program

A.1.10 Package items
package_item ::=
package_or_generate_item_declaration
| specparam_declaration
| anonymous_program
| timeunits_declaration

But in the LRM there is not a single sentence for the purpose and the usage
of this construct.
Can anyone help me in understanding the usage and semantics of this.

Thanks
Kausik Datta