Plotting and printing functions may search for the tit
attribute or even for the doc attribute, depending on
c.env$docout.
doc(x) <- text will append the existing doc(x) text to
the new text unless its first element equals (the first element
of) text.
(This avoids piling up the same line by unintended multiple call to
doc(x) <- value with the same value.)
If the first element of text equals "^",
the first element of doc(x) is dropped.
tit(x) <- string replaces tit(x) with string.