This is a template!

What happens when we lock two different consequent sub blocks:

<!--SUB:sub1-->
  This is mixed: <!--KEY:id-->!
<!--END:sub1-->

Now comes sub2:

<!--SUB:sub2-->
  This is mixed: <!--KEY:id-->!
<!--END:sub2-->

As you can see to make mixed rows we really have to enclose
them both in a third sub block. When instance is called
the output is added to where the template is.

There are actually two different ways to lock a sub blocks -
front or back. Lets demonstrate it with a confusing example.

<!--SUB:counter--> Counting: <!--KEY:id-->
<!--END:counter-->

By default the locking happens at end. In practice you rarely
need locking at front but it is useful sometimes.