In PHP, objects are they passed by value or by reference?

[seo.gops]

In PHP, objects are they passed by value or by reference?

[kajalescort]

One of the key-points of PHP OOP that is often mentioned is that "objects are passed by references by default". ... A PHP reference is an alias, which allows two different variables to write to the same value. In PHP, an object variable doesn't contain the object itself as value.