What's the coding standard for class constants?
The correct one would be:

class Foo {
  const CONSTANT_VALUE = 'bar';
}


For example, quoting after Zend Framework naming conventions (however there are many others for different frameworks, just Google around):


  Constants may contain both alphanumeric characters and underscores.
  Numbers are permitted in constant names.
  
  All letters used in a constant name must be capitalized, while all
  words in a constant name must be separated by underscore characters.
  
  For example, EMBED_SUPPRESS_EMBED_EXCEPTION is permitted but
  EMBED_SUPPRESSEMBEDEXCEPTION is not.
  
  Constants must be defined as class members with the "const" modifier.
  Defining constants in the global scope with the "define" function is
  permitted but strongly discouraged.


It does not explicitely say anything about FOO_CONSTANT_VALUE vs CONSTANT_VALUE, but not using class name in constant name is general practice. Which perfectly makes sense, considering that you are in class scope.