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=head1 DESCRIPTION
This document describes the form of a parse tree as used between the various Zoidberg objects.
=head2 Example
 # Commandline input:
  
 $ ls -al | perl{ while (<STDIN>) { print $_ }  }abc && echo done
  
 # Would be parsed to:
  
 [ 
        [qw/SH ls -al/],
        [ [qw/PERL abc/], q{ while (<STDIN>) { print $_ } } ],
        'AND',
        [qw/SH echo done/]
 ]
  
  
  
 # Commandline input:
  
 $ cd .. && ls -al ; cp dus ~/tmp/ &
  
 # Would be parsed to:
  
 [
        [qw/CMD cd ../],
        'AND',
        [qw/SH ls -al/],
        'EOS',  # End Of Statement
        [qw{SH cp dus ~/tmp/}],
        'BGS'   # BackGround Statement
 ]
   
 # FIXME an example with redirections
=head2 Basics 
A parse tree is an array consisting of blocks and tokens. A block can be any kind of code and is stored in
a nested array. Blocks directly following each other are supposted to be a pipeline. A token is a delimiter 
between blocks.
The first field of a block contains information about the block, all other field in a block make up the content.
The most important information about a block is the context, which tells the parser how to execute the block.
This first field can be: 
 a scalar       ==> it is the context name
 a nested array ==> the first field is the context name
 a nested hash  ==> the key 'context' contains the context name
You are  free to store all kinds of specific information in this first field as long as it contains a context name.