A data frame where each row is a CDI item and each column is a
variable about it: item_id
, item_kind
(e.g. word, gestures,
word_endings), item_definition
, english_gloss
,
language
, form
, form_type
, category
(meaning-based group as shown on the CDI form), lexical_category
,
lexical_class
, complexity_category
, uni_lemma
).