This may be implementation-specific, but in general, the initial selected option depends on the initial instance data. This means: If the instance node the xforms:select1
is bound to is empty, and the xforms:itemset
of the select1 doesn't contain an item with an empty value, no option will be selected. The same should be true if there's an initial instance value, but no item in the itemset with a corresponding value.
I've tested this with Orbeon, maybe other implementations behave else. Anyway, the described behaviour is described also in the XForms 1.1 Specifications (see the paragraphs starting with "For closed / open selections"), so i would expect it to be the default behaviour.