Currently, there are (in particular numeric) vector types (postfix -vector) in the CLI spec. However, even with the default value (which is optional), there is no way to know whether the number of entries is allowed to change.

E.g. a vector specifying parameters for each of a variable number of registration stages must have an arbitrary number of comma-separated entries, but a 3D point vector could be more conveniently displayed in the GUI with a fixed number of X,Y,Z edit widgets.

For embedding CLI modules in MeVisLab, this is also relevant because there are already separate parameter field types for 2/3/4-dimensional vectors (with corresponding specialized edit widgets).

I suggest to just add an optional, integer-valued "dimensions" attribute to the (numeric) vector types. If it is not present (or not supported), the parameter would be presented as a variable-dimensionality, comma-separated value, exactly like now.