what is java:comp/env?
===

what is meant by `java:comp/env` ? 

What does the look up like :

    Context envContext = (Context)initContext.lookup("java:comp/env");

do ?

I understand that a look-up like :

    (DataSource)envContext.lookup("jdbc/MyDatasource")

looks up for the name `MyDatasource` in the `context.xml` or `web.xml` to get the URL of the database. _Is it so ? !!_ But what does the former look up do ?

