Not possible to use conditions for show parameters in doctab UIX

The docextra UIX (https://www.xwiki.org/xwiki/bin/view/Documentation/DevGuide/ExtensionPoint/Document%20Docextra/) allows to inject new tabs in pages and provide a parameter show allowing to chose to display or not the tab.
However it's actually not possible to play with this parameter value: it's only if the parameter is missing that the tab won't be shown. Using false won't hide it.

The reason is that all parameters are interpreted as String values and we only use a boolean condition in our template.