CONSTANTS and PHP Class Definitions. Using define('MY_VAR', 'default value'). INSIDE a class definition does not work as expected. You have to use the PHP keyword 'const' and initialize it with a scalar value -- boolean, int, float, string (or array in PHP 5.6+) -- right away.
Prepositional Phrases. Do not use a comma between separate phrases unless they are in a series. A comma may also set off a single prepositional phrase at the beginning to make the sentence clear. A comma is recommended after any introductory prepositional phrase of more than four words. Correct: Under the kitchen table the dog cowered. (Single short, clear phrase.
The Quick Answer. When a word like and, or, and but (called conjunctions) joins two independent clauses (i.e., clauses that could stand alone as sentences), you should put a comma before it. Put a Comma before a Conjunction If It Joins Two Independent Clauses. Words like and, or, and but are known as conjunctions.