Possibility to show DemoSource depending on Vaadin version

[paodb]

As many add-ons support different Vaadin versions, it could be possible to need to show an extra source code that its different depending on the Vaadin version (for example stylesheets). So it would be nice to have the possibility to say "only show this source code if Vaadin version is X". Something similar to the use of // #if vaadin eq 24 to show lines of the code only when the specific vaadin version is in use.