InjectTag currently works only for unpaired tags (<mgnl:includeuri .../>)
If we would be able to replace also content between pair tags, we can also leave the original snippet content in place as fallback.

<mgnl:includeuri>
some (probably obsolete) area or component content cached with a page
</mgnl:includeuri>

The main reason is to skip time consuming snippet injection if the content doesn't come from cache but directly from rendering. We need to mark content comming from cache (to be addressed by MGNLCACHE-81).