You probably noticed that most lines in the various blocks of code on this website end in a semicolon (if you ignore the comments). Basically the semicolon separates statements in the code, similar to periods in a sentence, so After Effects doesn’t get confused by a single, long run-on sentence. While writing the code as a single line does require the use of a semicolon between statements, that’s not always true when you place line breaks between them.
So what’s the deal, you may be asking, when do I know when I have to use a semicolon? I’ll get to that, but first do know that many people who code place a semicolon at the end of a line no matter what. I’m one of those people, so that’s the way I write expressions. If the line ends in an open or closed curly bracket, or it’s a single line of code, or it’s the last line of code, I’ll usually leave off the semicolon. This is acceptable practice if you would like to go this route.
R=12 L=13 R //No semicolon is required for lines 1-3. The line breaks are read like semicolons because the character that follows the return can't be interpreted as a continuation of the previous line. //However R=12;L=13;R //Because line 6 contains several statements on one line, a semicolon is required to separate them.