The tWSDL API modelGroup::sequence::new is currently restricted to the case where all child elements are simpleTypes. This is a common use case. It is also restricted to a each child occurring zero or one time.
I know the API call seems simple enough, but it hides a lot of code generation, including the type validation routines and the invoke routine. These routines would look different than the simple case. This seems to suck pretty bad until you consider the number of Tcl API which take or return multi-dimensional data.
It turns out that type validation is the easiest to extend to multi-dimensional data, but overall, the problem is not too difficult and was planned for in advance.
This is the meaning of the {ElementA Value ElementB Value} configuration (called a conversionList). The modelGroup::sequence API assumes actual values for each child element. This configuration is used in the invoke API (which is auto-generated) by the API ::xml::childElementsAsListWithConversions
Currently this simple API only handles the Value type, although if you look at it, other types are commented about.
Let me just say that developing the type system and the API is very delicate, it has to reflect the method of type development used by XML-Schema, otherwise we cannot publish the interface in a way that a generic client can use. Beyond the simple interface, the developer must become more aware of how things work throughout the entire system and in XML-Schema, WSDL, etc.
I'll post another note about the invoke procedure interface, which is a key abstraction. Any developer using tWSDL for complex services must understand this interface.
