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usage(Topic [,allfiles:T]), topic a quoted or unquoted name of a help
usage(Topic1, Topic2, ... [,allfiles:F])

Keywords: general
usage(Topic) gives short usage information on Topic, where Topic is a
function or command or one of the general information topics such as
'options' or 'graph_keys'.

usage() works identically to help(), except it gives only a brief
summary of the topic, instead of all the detail.

usage() returns an "invisible" LOGICAL scalar whose value is True only
when at least one topic requested was found.  The value may be assigned
or tested but will not be printed automatically.  See topic

usage() scans the files NAMED in CHARACTER vector HELPFILES.  If the
current help file is not named in HELPFILES, it is scanned first.

If there is only one topic (the usual case), usage() scans files until
it finds the topic.  You can use 'allfiles:T' as an argument to force it
to search all the files in HELPFILES.

usage(topic1, topic2, ...) does the same except that all the files are
searched for the topics.  When you use 'allfiles:F' as an argument, no
additional files are searched once a topic has been found in a file.

For many commands and macros, help(topic, subtopic:"usage") provides
more complete usage information than does usage().

usage() is implemented as a macro which uses functions gethelp() and
getusage() to retrieve the information.  Functions getusage() and
gethelp() scan only a single file.

Prior to Version 4.12, function getusage() was named usage() and there
was no macro named usage().

See help(), getusage() and gethelp() for full details.  See topic
addhelpfile() for information on adding file names to HELPFILES.

Gary Oehlert 2003-01-15