Returns a string containing a string representation of all the array elements in the same order, with the glue string between each element.
注: implode() can, for historical reasons, accept its parameters in either order. For consistency with explode(), however, it may be less confusing to use the documented order of arguments.
注: As of PHP 4.3.0, the glue parameter of implode() is optional and defaults to the empty string(''). This is not the preferred usage of implode(). We recommend to always use two parameters for compatibility with older versions.