Of the two structural rules this one is much more commonly used in GroIMP. It replaces each instance of the pattern defined on the left side with the new created graph structure on the right side.

<pattern> ==> <structure>;

So if all A's in the model should be replaced by F's the patterns a the A's and the new structure is an F:

A ==> F;

The definition of the pattern that should be replaced can be defined by using xl syntax and xl-operators.

A[F] ==> F;

first((*A*)) ==> F;

Additionally the pattern can be defined using conditions:

A(1)==>F;

a:A,(a.len!=1)==>F;

A more complex structure can be created by using the turtle geometry and graph-syntax.

A ==> F [RL(90) F A] F +> A;

With the addition of modules and 3d objects more object oriented nodes can be added:

A ==> F [RL(90) Cylinder(1,4) A] F +> MyNewNode(2.4);

SPO: Single pushout graph rewriting