The following keywords are recognized:
string, the element to which this type applies is a string of binary
characters.
integer or int, the element to which this type applies is a whole
number or integer.
boolean or bool, the element to which this type applies only has state
true or false.
float or double, the element to which this type applies is a
continuous, or real, number.
object, the element to which this type applies is the instance of an
undetermined class.
mixed, the element to which this type applies can be of any type as
specified here. It is not known on compile time which type will be
used.
array, the element to which this type applies is an array of values,
see the section on Arrays for more details.
resource, the element to which this type applies is a resource per the
definition of PHP at
http://www.php.net/manual/en/language.types.resource.php.
void, this type is commonly only used when defining the return type of
a method or function. The basic definition is that the element
indicated with this type does not contain a value and the user should
not rely on any retrieved value.
null, the element to which this type applies is a NULL value or, in
technical terms, does not exist.
A big difference compared to void is that this type is used in any
situation where the described element may at any given time contain an
explicit NULL value.
callable, the element to which this type applies is a pointer to a function call. This may be any type of callback as
defined in the PHP manual at
http://php.net/manual/en/language.pseudo-types.php
false or true, the element to which this type applies will have the
value true or false. No other value will be returned from this
element.
This type is commonly used in conjunction with another type to
indicate that it is possible that true or false may be returned
instead of an instance of the other type.
self, the element to which this type applies is of the same Class, or
any of its children, as which the documented element is originally
contained.
