questions to tags /R/ and /T/



Hi,

Maxima sometimes appends some curious "tags" to the output 
expressions:

e.g. rat(x/y) produces the tag /R/ which obviously means a
              "canonical rational expression" (whatever that is).

     taylor(sin(x),x,0,3) produces the tag /T/ which obviously means
     "taylor series".

Those tags, which are assumedly not part of the expession itself,
can be removed by apply(op(..),args(...)).

Is there a general principle or a deeper mind for those tags?

What is the actual effect of them
(just appending + ... do the expression (for /T/), or even more)?

Where are those tags stored (if not as part of the expression)?

Are there more such tags than /R/ and /T/?

Thanks in advance for answers
Wilhelm Haager