Extensions to QueryPath should implement the QueryPathExtension interface. The only requirement is that the extension provide a constructor that takes a QueryPath object as a parameter.

Here is an example QueryPath extension:

In this example, the StubExtensionOne class implements QueryPathExtension. The constructor stores a local copyof the QueryPath object. This is important if you are planning on fully integrating with QueryPath's Fluent Interface.

Finally, the stubToe() function illustrates how the extension makes use of QueryPath internally, and remains part of the fluent interface by returning the $qp object.

Notice that beneath the class, there is a single call to register the extension with QueryPath's registry. Your extension should end with a line similar to this.

How is a QueryPath extension called?

QueryPath extensions are called like regular QueryPath functions. For example, the extension above can be called like this:

Since it returns the QueryPath ($qp) object, chaining is supported: When you write your own extensions, anything that does not need to return a specific value should return the QueryPath object. Between that and the extension registry, this will provide the best developer experience.