CHARACTERTEXT_KEY is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "DML Text Object" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_CHARACTERTEXT_KEY TYPE CHARACTERTEXT_KEY.
The CHARACTERTEXT_KEY table consists of various fields, each holding specific information or linking keys about DML Text Object data available in SAP. These include FRG_GUID (Set GUID), ELEMENT (MDF Text Element, like Set Type), SUBELEM (Subelement (Attribute of Set Type)), SUBOBJECT (Subobject, for example, row key of a set)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .