RenWenshan/emacs-lisp-intro-solutions — pull request #2 by mwfogleman (2014-03-17 15:37:38+00:00)
Title: Use buffer-substring-no-properties instead.

Chassell hints that you may want to use buffer-substring-no-properties instead of buffer-substring. This is because buffer-substring copies the text properties into the string, while buffer-substring-no-properties does not.