This is real simple. You might comment out code like this:

/*
 $thiscode = $is + $not + $interpreted;
*/

When you want to use that chunk of code, you'd remove the comments. That would require two deletions, and restoring would require adding four characters. Here's an alternative way:

/*
 $thiscode = $is + $not + $interpreted;
// */

Note that the double-slash comment doesn't actually get interpreted because it's inside the /* */ comment block. To uncomment it:

//*
 $thiscode = $is + $interpreted;
// */