Templates are neither necessary nor sufficient for separating model and view (presentation). Not necessary because the separation is really accomplished by the model/view protocol, and not sufficient because presentation code can always seep into the model code. In fact, the StringTemplate approach requires complex views to be implemented in the model code.
A great m/v separation may be achieved by just having separate code for model and for view, even in the same language. The only requirements are on the data passed from the model to the view:
- it should be available before the view code runs
- it should consist only of lists of lists, and lists of opaque objects
It's probably worth noting explicitly that the view depends on the model and not vice versa.
The StringTemplates author acknowledges that his solution is insufficient to keep view logic out of the model code. The model code could pass data like "the color red" to the view layer. Since StringTemplates is such a simple language, more complex view features must be implemented with the help of model code. Any possible document may be generated, but only with the help of the model code.
So if m/v separation isn't the point of templates, what is? Separation of roles. The roles of programmer and designer aren't necessarily performed by different people, but they do require different approaches. The designer role includes everything that can be done in a WYSIWYG editor, with all visible elements, "includes", and conditionals. As document formats evolve, this could become part of the normative editor functionality. CSS visibility could be hacked to support conditionals, and XInclude takes care of the rest.