*** Guide-to-Links ***
ID is a special class of link-types that is generated by the
parser for idiomatic strings listed in the dictionary.

        at_hand in_store: MVp- or Mp- or Pp-...

               |  |    |
        Peace is at  hand

Note that the "IDTB" link used here is not explicitly listed in
the dictionary. Rather, the phrase "at_hand" is simply listed as
an idiomatic string. In reading in the dictionary, the parser
generates arbitrary link names, always beginning with the letters
"ID", to link the words of the idiom together.

Little can be said in general about idiomatic expressions.
Probably the largest category are prepositional-phrase-like
constructions which cannot be handled as ordinary
prepositional phrases for some reason. In the case of "at
hand", for example, the singular noun "hand" normally requires
a determiner. Some idioms are more like adverbs, in that they
cannot be complements of "be": "by_car", "in_turn". Some are
actually like prepositions, modifying a noun or verb and
taking another noun as an object: "next_to", "in_back_of". And
some are like conjunctions, taking a clausal complement:
"now_that", "in_case". The dictionary also includes a few
idiomatic noun phrases ("head_of_state") and verbs ("do_so").

Grammar Documentation Page.