Writers have to be careful and insert the comma when it is necessary for readability. In San Antonio jazz and mariachi bands vie for prominence. When you revise your text for comma punctuation, one thing to do is to ask yourself whether your reader would be able to process your sentence. Try reading your text aloud and see where you take breaks and pause. In non-technical writing the comma is more of an option in this case than it is in legal writing.
Writers can signal non-essential or explanatory information with a pair of commas.
Consider the following examples It is up to Congress, not the courts, to change the law. The new crop, however good it may be, will have to be replaced. The commas in the above examples mark the boundaries of the interrupting phrase. One way to remember whether to use two commas in instances of setting off information is to think of the commas as parentheses. A neighbor who lived next door for three years was a passenger on flight 800.