Effect of Readtable Case on the Lisp Reader (ANSI and GNU Common Lisp Document)

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#### 23.1.2 Effect of Readtable Case on the Lisp Reader

The readtable case of the current readtable affects the Lisp reader in the following ways:

`:upcase`

  When the readtable case is `:upcase`, unescaped constituent characters are converted to uppercase, as specified in Reader Algorithm.

`:downcase`

  When the readtable case is `:downcase`, unescaped constituent characters are converted to lowercase.

`:preserve`

  When the readtable case is `:preserve`, the case of all characters remains unchanged.

`:invert`

  When the readtable case is `:invert`, then if all of the unescaped letters in the extended token are of the same case, those (unescaped) letters are converted to the opposite case.