In Markua, you can add special comment lines to your code samples:

"The magic words are markua-start-insert, markua-end-insert, markua-start-delete and markua-end-delete. Any line containing one of those words will be removed completely by Leanpub before being inserted into the output."

These instructions apply specifically to code samples. So, if you write this:

That will produce this in the book:
​

So, the lines with markua-start-insert, markua-end-insert, markua-start-delete, and markua-end-delete, do not appear in the code samples in the book.

Please note that by design, syntax highlighting does not work when you use these features, mostly so the insertion and the deletion stand out more.