The last sentence,
You should not use this trick, unless you first publish a library that abstracts it away.
means that if you do something that simulates global lexical variables, then the implementation of that simulation should not be apparent to the user. For instance, you might simulate a global lexical using some scheme using define-symbol-macro
, but if you do, it should be transparent to the user. See Ron Garret's GLOBALS — Global Variables Done Right for an example of “a library that abstracts it away.”