Callbacks
Type Juggling
Types
PHP Manual

## Pseudo-types and variables used in this documentation

### mixed

mixed indicates that a parameter may accept multiple (but not necessarily all) types.

gettype() for example will accept all PHP types, while str_replace() will accept strings and arrays.

### number

number indicates that a parameter can be either integer or float.

### callback

callback pseudo-types was used in this documentation before callable type hint was introduced by PHP 5.4. It means exactly the same.

### void

void as a return type means that the return value is useless. void in a parameter list means that the function doesn't accept any parameters.

### ...

`$...` in function prototypes means and so on. This variable name is used when a function can take an endless number of arguments.

Callbacks
Type Juggling
Types
PHP Manual