This is used to assign values to the templates by reference instead
of making a copy. See the PHP manual on variable referencing for an
explanation.
采用引用的方式赋值到模板中，而不是在模板中创建一个数值的副本。引用的概念可以查看PHP手册的变量引用部分。
Technical Note: This is used to assign values to the templates by reference. If you assign a variable by reference then change its value, the assigned value sees the change as well. For objects, assign_by_ref() also avoids an in-memory copy of the assigned object. See the PHP manual on variable referencing for an in-depth explanation.
注意：本函数用于采用引用的方式赋值到模板中。如果把一个 变量采用引用的方式赋值后，变量的值又被改变了，那么在模板中将会看到变量改变后的值。对于对象，assign_by_ref()函数也避免了对象的内存 拷贝。进一步的解释可以查看PHP手册的变量引用部分。