2.2.2 [W3C-XSS] Section 3.8.4, Model Group Validation Rules
V0011:
-
Nothing in the above should be understood as ruling out groups whose {particles} is empty: although no sequence can be ·valid· with respect to such a group whose {compositor} is choice, the empty sequence is ·valid· with respect to empty groups whose {compositor} is sequence or all.
MSXML6
An empty group that has a {compositor} property with
a value of choice
can be valid.