100 lines
3.6 KiB
Plaintext
100 lines
3.6 KiB
Plaintext
.\" This module is believed to contain source code proprietary to AT&T.
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.\" Use and redistribution is subject to the Berkeley Software License
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.\" Agreement and your Software Agreement with AT&T (Western Electric).
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.\"
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.\" @(#)tt13 8.1 (Berkeley) 6/8/93
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.\" Copyright (C) Caldera International Inc. 2001-2002. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions are
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.\" met:
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.\"
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.\" Redistributions of source code and documentation must retain the above
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.\" copyright notice, this list of conditions and the following
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.\" disclaimer.
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.\"
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.\" Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\"
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.\" This product includes software developed or owned by Caldera
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.\" International, Inc. Neither the name of Caldera International, Inc.
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.\" nor the names of other contributors may be used to endorse or promote
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.\" products derived from this software without specific prior written
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.\" permission.
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.\"
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.\" USE OF THE SOFTWARE PROVIDED FOR UNDER THIS LICENSE BY CALDERA
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.\" INTERNATIONAL, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL CALDERA INTERNATIONAL, INC. BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) RISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
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.\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.NH
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Environments
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.PP
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As we mentioned, there is a potential problem
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when going across a page boundary:
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parameters like size and font
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for a page title may well be different from those
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in effect in the text when the page boundary occurs.
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.UL troff
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provides a very general way to deal with this and
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similar situations.
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There are three `environments',
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each of which has independently settable versions of
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many of the parameters associated with processing,
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including size, font, line and title lengths,
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fill/nofill mode, tab stops, and even partially collected lines.
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Thus the titling problem may be readily solved by processing the main text
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in one environment and titles in a separate one
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with its own suitable parameters.
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.PP
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The command
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.BD .ev\ n
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shifts to environment
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.BD n ;
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.BD n
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must be 0, 1 or 2.
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The command
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.BD .ev
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with no argument returns to the
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previous environment.
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Environment names are maintained in a stack, so calls
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for different environments may be nested and unwound consistently.
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.PP
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Suppose we say that the main text is processed in environment 0,
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which is where
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.UL troff
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begins by default.
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Then we can modify the new page macro
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.BD .NP
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to process titles in environment 1 like this:
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.P1 2
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^de NP
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^ev 1 \e" shift to new environment
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^lt 6i \e" set parameters here
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^ft R
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^ps 10
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\&... any other processing ...
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^ev \e" return to previous environment
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^^
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.P2
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It is also possible to initialize the parameters for an environment
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outside the
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.BD .NP
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macro,
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but the version shown keeps all the processing in one place
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and is thus easier to understand and change.
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