    def count_vocab_items(self, counter: Dict[str, Dict[str, int]]):
        """
        If there are strings in this field that need to be converted into integers through a
        :class:`Vocabulary`, here is where we count them, to determine which tokens are in or out
        of the vocabulary.

        If your `Field` does not have any strings that need to be converted into indices, you do
        not need to implement this method.

        A note on this `counter`: because `Fields` can represent conceptually different things,
        we separate the vocabulary items by `namespaces`.  This way, we can use a single shared
        mechanism to handle all mappings from strings to integers in all fields, while keeping
        words in a `TextField` from sharing the same ids with labels in a `LabelField` (e.g.,
        "entailment" or "contradiction" are labels in an entailment task)

        Additionally, a single `Field` might want to use multiple namespaces - `TextFields` can
        be represented as a combination of word ids and character ids, and you don't want words and
        characters to share the same vocabulary - "a" as a word should get a different id from "a"
        as a character, and the vocabulary sizes of words and characters are very different.

        Because of this, the first key in the `counter` object is a `namespace`, like "tokens",
        "token_characters", "tags", or "labels", and the second key is the actual vocabulary item.
        """
        pass
If there are strings in this field that need to be converted into integers through a
:class:`Vocabulary`, here is where we count them, to determine which tokens are in or out
of the vocabulary.

If your `Field` does not have any strings that need to be converted into indices, you do
not need to implement this method.

A note on this `counter`: because `Fields` can represent conceptually different things,
we separate the vocabulary items by `namespaces`.  This way, we can use a single shared
mechanism to handle all mappings from strings to integers in all fields, while keeping
words in a `TextField` from sharing the same ids with labels in a `LabelField` (e.g.,
"entailment" or "contradiction" are labels in an entailment task)

Additionally, a single `Field` might want to use multiple namespaces - `TextFields` can
be represented as a combination of word ids and character ids, and you don't want words and
characters to share the same vocabulary - "a" as a word should get a different id from "a"
as a character, and the vocabulary sizes of words and characters are very different.

Because of this, the first key in the `counter` object is a `namespace`, like "tokens",
"token_characters", "tags", or "labels", and the second key is the actual vocabulary item.
allennlp/data/fields/field.py