'Run processor. Must be overridden by subclasses.
When the parser determines the appropriate type of a block, the parser
will call the corresponding processor\'s ``run`` method. This method
should parse the individual lines of the block and append them to
the etree.
Note that both the ``parent`` and ``etree`` keywords are pointers
to instances of the objects which should be edited in place. Each
processor must make changes to the existing objects as there is no
mechanism to return new/different objects to replace them.
This means that this method should be adding SubElements or adding text
to the parent, and should remove (``pop``) or add (``insert``) items to
the list of blocks.
Keywords:
* ``parent``: A etree element which is the parent of the current block.
* ``blocks``: A list of all remaining blocks of the document.'

def run(self, parent, blocks):

    pass
