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This line is less than 72 characters, and should not be split.
Neither should this line.

This line contains exactly 72 characters, and so it should not be split.

This line is just over 72 characters; the last word should be on a new line.

On this line the 72nd character is a space, consequently the last seven words should be on a new line.

On this line the 73nd character is a space, therefore the last six words should be on a new line.

     This is an indented line, and when it is split the following line should be indented the same amount.

This is a very long line that isn't indented at all. The purpose of this line is to make sure that a line can be broken more than once. When this line is wrapped, it should produce four lines, and I'm putting in enough words to make sure that that's what happens.

    This is the same line as before, but it is indented. The purpose of this line is to make sure that a line can be broken more than once. When this line is wrapped, it should produce four lines, and I'm putting in enough words to make sure that that's what happens.
    
Amazon in particular has some long URLs, such as http://www.amazon.com/Schaums-Outline-Data-Structures-Java/dp/0071476989/ref=sr_1_3?ie=UTF8&s=books&qid=1227652790&sr=1-3, which cannot be conveniently split.