LastMitch is perfectly correct.. Ask the author first..
To give you the general idea of what it is, it can be explain as simple as this..
This process is also called chaining.. However, if it is not a class, but instead they are both methods of the same class, then the expression you have provided is perfectly wrong. Because $this->class() cannot be called within other class unless it is extended or it is an statically declared from somewhere. If they are both methods of the same class or the other is method of a parent class then the declaration should be somethin like this.