The mentioned article is for X-Cart 5.2.x only.
For X-Cart 5.3.x you should check this one:
http://devs.x-cart.com/en/basics/adding_new_property_to_a_product/adding_product_property_via_formmodel_api.html
"Compose" methods are used to "group" multiple fields into a single line. For example, you want to add a custom field and display it to the right of the existing Price field. In this case you "compose" your custom field with the Price field.
If your custom field should be displayed alone on a new form line, you don't need "compose" methods.