Why does the Zend framework prepend an underscore here?

Question

What's the point of having $_comment instead of $comment?

class Default_Model_Guestbook
{
    protected $_comment;
    protected $_created;
    protected $_email;
    protected $_id;
    protected $_mapper;

Answer 1

Prefixing protected and private class variables is a common convention in PHP. It makes it easier to distinguish between those that are public and those that are protected or private.