\Header{help}{Documentation}
\alias{?}{help}
\keyword{documentation}{help}
\begin{Description}\relax
These functions provide access to documentation.
Documentation on a topic with name \code{name} (typically, an \R{}
object or a data set) can be printed with either \code{help(name)} or
\code{?name}.\end{Description}
\begin{Usage}
\begin{verbatim}
help(topic, offline = FALSE, package = .packages(),
     lib.loc = NULL, verbose = getOption("verbose"),
     try.all.packages = getOption("help.try.all.packages"),
     htmlhelp = getOption("htmlhelp"),
     pager = getOption("pager"))
?topic
type?topic
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{topic}] a name or character string on which documentation is
sought (but \emph{not} a variable containing a character string!).
\item[\code{offline}] a logical indicating whether documentation should be
displayed on-line to the screen (the default) or hardcopy of it
should be produced.
\item[\code{package}] a name or character vector giving the packages to look
into for documentation.  By default, all packages in the search path
are used.
\item[\code{lib.loc}] a character vector of directory names of \R{} libraries,
or \code{NULL}.  The default value of \code{NULL} corresponds to all
libraries currently known.  If the default is used, the loaded
packages are searched before the libraries.
\item[\code{verbose}] logical; if \code{TRUE}, the file name is reported.
\item[\code{try.all.packages}] logical; see \code{Notes}.
\item[\code{htmlhelp}] logical (or \code{NULL}).  If \code{TRUE} (which is the
default after \code{\Link{help.start}} has been called), the HTML
version of the help will be shown in the browser specified by
\code{options("browser")}. See \code{\Link{help.start}} for details
of the browsers that are supported. 
\item[\code{pager}] the pager to be used for \code{\Link{file.show}}.
\item[\code{type}] the special type of documentation to use for this topic;
for example, if the type is \code{class}, documentation is
provided for the class with name \code{topic}.  The function
\code{topicName} returns the actual name used in this case.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
In the case of unary and binary operators and control-flow special
forms, the name may need to be quoted.

If \code{offline} is \code{TRUE}, hardcopy of the documentation is
produced by running the LaTeX version of the help page through
\code{latex} (note that LaTeX 2e is needed) and \code{dvips}.
Depending on your \code{dvips} configuration, hardcopy will be sent to
the printer or saved in a file.  If the programs are in non-standard
locations and hence were not found at compile time, you can either set
the options \code{latexcmd} and \code{dvipscmd}, or the environment
variables \code{R\_LATEXCMD} and \code{R\_DVIPSCMD} appropriately.
The appearance of the output can be customized through a file
\file{Rhelp.cfg} somewhere in your LaTeX search path.\end{Details}
\begin{Note}\relax
Unless \code{lib.loc} is specified explicitly, the loaded packages are
searched before those in the specified libraries.  This ensures that
if a library is loaded from a library not in the known library trees,
then the help from the loaded library is used.  If \code{lib.loc} is
specified explicitly, the loaded packages are \emph{not} searched.

If this search fails and argument \code{try.all.packages} is
\code{TRUE} and neither \code{packages} nor \code{lib.loc} is
specified, then all the packages in the known library trees are
searched for help on \code{topic} and a list of (any) packages where
help may be found is printed (but no help is shown).
\bold{N.B.} searching all packages can be slow.

The help files can be many small files.  On some file systems it is
desirable to save space, and the text files in the \file{help} directory
of an installed package can be zipped up as a zip archive
\file{Rhelp.zip}. Ensure that file \file{AnIndex} remains un-zipped.
Similarly, all the files in the
\file{latex} directory can be zipped to \file{Rhelp.zip}.\end{Note}
\begin{SeeAlso}\relax
\code{\Link{help.search}()} for finding help pages on a ``vague'' topic.
\code{\Link{help.start}()} which opens the HTML version of the \R{}
help pages;
\code{\Link{library}()} for listing available packages and the
user-level objects they contain;
\code{\Link{data}()} for listing available data sets;
\code{\Link{methods}()}.

See \code{\Link{prompt}()} to get a prototype for writing \code{help}
pages of private packages.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
help()
help(help)              # the same

help(lapply)
?lapply                 # the same

help("for")             # or ?"for", but the quotes are needed
?"+"

help(package = stepfun) # get help even when package is not loaded

data()                  # list all available data sets
?women                  # information about data set "women"

topi <- "women"
help(topi) ##--> Error: No documentation for `topi'

try(help("bs", try.all.packages=FALSE)) # reports not found (an error)
help("bs", try.all.packages=TRUE) # reports can be found in package `splines'
\end{ExampleCode}
\end{Examples}

