The CTX_ANL package is used with AUTO_LEXER and provides procedures for adding and dropping a custom dictionary from the lexer. A custom dictionary might be one that you develop for a special field of study or for your industry. In most cases, the dictionaries supplied for the supported languages with Oracle Text are more than sufficient to handle your requirements.
For a complete description of this package within the context of Oracle Text, see CTX_ANL in the Oracle Text Reference.