XTCE13 — Variable string size specification enforces one of DynamicValueType or DiscreteLookupListType

In addition to the clarity issues highlighted by XTCE13-30, the current definition of StringDataEncoding has a major drawback for variable strings: the VariableStringType enforces one of DynamicValueType or DiscreteLookupListType.

However the size of the string can be very well determined by the other two methods LeadingSize or TerminationChar. Usage of LeadingSize/TerminationChar in combination with the enforced DynamicValueType/DiscreteLookupListType does not make sense when the string fills completely the allocated buffer and so the size of the string determines the size of the buffer.

In my opinion having a variable size buffer with a variable string inside that buffer is much less common (never heard of it in fact) than having a fixed size buffer with a variable string inside or a variable string with no buffer (the buffer is the string).

Suggest to make the DynamicValueType/DiscreteLookupListType optional.