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When adding the validator for "Fix Versions" field as shown below you have also option to disallow released versions. In ideal situation fix version should be a version which is not already released. You fix issues and assign fix version to them, or you schedule issues to feature releases using fix version. In these cases it is logical that fix version is not a released version. Note that version validity check for the selected component is done whether you click this checkbox or not.
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Similarly the validator for the "Affects Versions" field as shown below allows you to disallow unreleased versions. For most of the time this is the wanted behavior. Users should not be able to report bugs for a version which is not released. Note that version validity check for the selected component is done whether you click this checkbox or not.
There are two modes for this validator. In both modes it ensures selected versions are valid for selected components. Note that add-on setting “Which versions are valid when multiple component is selected” setting also affects which versions are considered valid.
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In the following screenshot the validator is added twice for each version field.
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