Description:
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The SPL exception definitions in the official manual are too ambiguous. As I talked to programmers, I noticed that many have problems with understanding, how to use them properly. Furthermore, the older documentation was more precise here and I think the authors should seriously consider writing something more about them.

Here's, what should be added:

LogicException:

 - Description: "Exception that represents error in the program logic. This kind of exceptions should directly leed to a fix in your code."
 - Source: copied from http://www.php.net/~helly/php/ext/spl/classLogicException.html

OutOfRangeException:

 - here, the description is completely wrong and makes no sense, if we look at the class diagram. According to docs.php.net, this class should extend RuntimeException, not LogicException.
 - Valid description: "Exception thrown when an illegal index was requested. This represents errors that should be detected at compile time."
 - Source: copied from http://www.php.net/~helly/php/ext/spl/classOutOfRangeException.html

RangeException:

 - identical case, as OutOfRangeException
 - Valid description: "Exception thrown to indicate range errors during program execution. Normally this means there was an arithmetic error other than under/overflow. This is the runtime version of DomainException."
 - Source: copied from http://www.php.net/~helly/php/ext/spl/classRangeException.html

OutOfBoundsException:

 - "This represents errors that cannot be detected at compile time." should be added, as it is in http://docs.php.net/manual/en/class.outofboundsexception.php

UnexpectedValue:

 - "Typically this happens when a function calls another function and espects the return value to be of a certain type or value not including arithmetic or buffer related errors." should be added, as it is in http://docs.php.net/manual/en/class.unexpectedvalueexception.php

LogicException:

 - The old documentation at http://www.php.net/~helly/php/ext/spl/ and the official one say two completely different things about this exception. Decide: does it mean that the specified length makes no sense (i.e. because it is negative, and length cannot be negative), or that some value has an invalid length, but then - why does it extend LogicException in this case? If it extends, it should be clarified that it should be only used on errors in the program logic, not to validate user data.