The declare structure is used to set execution instructions for a piece of code

Declare

(PHP 4, PHP 5, PHP 7)

The declare structure is used to set execution instructions for a piece of code. The syntax of declare is similar to other process Control structures:

DECLARE (Directive)    statement

The Directive section allows you to set the behavior of the declare code snippet. Currently only two commands are known:ticks(see ticks instructions below for more information) and encoding(see encoding instructions below for more information).

http://php.net/manual/zh/control-structures.declare.php

The declare structure is used to set execution instructions for a piece of code