code: public DocxStamperConfiguration exposeInterfaceToExpressionLanguage(Class<?> interfaceClass, Object implementation) {
      this.expressionFunctions.put(interfaceClass, implementation);
      return this;
    }
docs: Exposes all methods of a given interface to the expression language.
  @param interfaceClass the interface whose methods should be exposed in the expression language.
  @param implementation  the implementation that should be called to evaluate invocations of the interface methods
  within the expression language. Must implement the interface above.