Initial checkin: 4.4BSD version. These files need to be updated with

current license information and adapted to the FreeBSD build
environment before they will build.

Approved by:    David Taylor <davidt@caldera.com>

1 files changed, 63 insertions, 0 deletions

diff --git a/share/doc/usd/22.trofftut/tt13 b/share/doc/usd/22.trofftut/tt13
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+.\" This module is believed to contain source code proprietary to AT&T.
+.\" Use and redistribution is subject to the Berkeley Software License
+.\" Agreement and your Software Agreement with AT&T (Western Electric).
+.\"
+.\"	@(#)tt13	8.1 (Berkeley) 6/8/93
+.\"
+.\" $FreeBSD$
+.NH
+Environments
+.PP
+As we mentioned, there is a potential problem
+when going across a page boundary:
+parameters like size and font
+for a page title may well be different from those
+in effect in the text when the page boundary occurs.
+.UL troff
+provides a very general way to deal with this and
+similar situations.
+There are three `environments',
+each of which has independently settable versions of
+many of the parameters associated with processing,
+including size, font, line and title lengths,
+fill/nofill mode, tab stops, and even partially collected lines.
+Thus the titling problem may be readily solved by processing the main text
+in one environment and titles in a separate one
+with its own suitable parameters.
+.PP
+The command
+.BD .ev\ n
+shifts to environment
+.BD n ;
+.BD n
+must be 0, 1 or 2.
+The command
+.BD .ev
+with no argument returns to the
+previous environment.
+Environment names are maintained in a stack, so calls
+for different environments may be nested and unwound consistently.
+.PP
+Suppose we say that the main text is processed in environment 0,
+which is where 
+.UL troff
+begins by default.
+Then we can modify the new page macro
+.BD .NP
+to process titles in environment 1 like this:
+.P1 2
+^de NP
+^ev 1	\e" shift to new environment
+^lt 6i	\e" set parameters here
+^ft R
+^ps 10
+\&... any other processing ...
+^ev	\e" return to previous environment
+^^
+.P2
+It is also possible to initialize the parameters for an environment
+outside the
+.BD .NP
+macro,
+but the version shown keeps all the processing in one place
+and is thus easier to understand and change.