\Header{terms.object}{Description of Terms Objects}
\keyword{models}{terms.object}
\begin{Description}\relax
An object of class \code{\Link{terms}} holds information about a
model.  Usually the model was specified in terms of a
\code{\Link{formula}} and that formula was used to determine the terms
object.

The object itself is simply the formula supplied to the call of
\code{\Link{terms.formula}}.  The object has a number of attributes
and they are used to construct the model frame.\end{Description}
\begin{Value}
An object with the following attributes:
\begin{ldescription}
\item[\code{factors}] A matrix of variables by terms showing which variables
appear in which terms.
\item[\code{term.labels}] A character vector containing the labels for each
of the terms in the model.
\item[\code{variables}] A list of the variables in the model
\item[\code{intercept}] Either 0, indicating no intercept is to be fit, or 1
indicating that an intercept is to be fit.
\item[\code{order}] A vector of the same length as \code{term.labels}
indicating the order of interaction for each term 
\item[\code{response}] The index of the variable (in variables) of the
response (the left hand side of the formula).
\item[\code{offset}] If the model contains \code{\Link{offset}} terms there
is an \code{offset} attribute indicating which terms are offsets
\item[\code{specials}] If the \code{specials} argument was given to
\code{\Link{terms.formula}} there is a \code{specials} attribute, a
list of vectors indicating the terms that contain these special
functions.
\end{ldescription}


The object has class \code{c("terms", "formula")}.\end{Value}
\begin{Note}\relax
These objects are different from those found in S.  In particular
there is no \code{formula} attribute, instead the object is itself a
formula.  Thus, the mode of a terms object is different as well. 

An example of the \code{specials} argument can be seen in the
\code{\Link{aov}} function.\end{Note}
\begin{SeeAlso}\relax
\code{\Link{terms}},
\code{\Link{terms.default}},
\code{\Link{formula}}.\end{SeeAlso}

