[unix-history] / usr / share / doc / usd / 22.trofftut / tt13

.\" 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
.\"
.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.
Commit	Line	Data
ad787160 C	1	.\" This module is believed to contain source code proprietary to AT&T.
	2	.\" Use and redistribution is subject to the Berkeley Software License
	3	.\" Agreement and your Software Agreement with AT&T (Western Electric).
ff262511	4	.\"
ad787160	5	.\" @(#)tt13 8.1 (Berkeley) 6/8/93
f9b4797c KD	6	.\"
	7	.NH
	8	Environments
	9	.PP
	10	As we mentioned, there is a potential problem
	11	when going across a page boundary:
	12	parameters like size and font
	13	for a page title may well be different from those
	14	in effect in the text when the page boundary occurs.
	15	.UL troff
	16	provides a very general way to deal with this and
	17	similar situations.
	18	There are three `environments',
	19	each of which has independently settable versions of
	20	many of the parameters associated with processing,
	21	including size, font, line and title lengths,
	22	fill/nofill mode, tab stops, and even partially collected lines.
	23	Thus the titling problem may be readily solved by processing the main text
	24	in one environment and titles in a separate one
	25	with its own suitable parameters.
	26	.PP
	27	The command
	28	.BD .ev\ n
	29	shifts to environment
	30	.BD n ;
	31	.BD n
	32	must be 0, 1 or 2.
	33	The command
	34	.BD .ev
	35	with no argument returns to the
	36	previous environment.
	37	Environment names are maintained in a stack, so calls
	38	for different environments may be nested and unwound consistently.
	39	.PP
	40	Suppose we say that the main text is processed in environment 0,
	41	which is where
	42	.UL troff
	43	begins by default.
	44	Then we can modify the new page macro
	45	.BD .NP
	46	to process titles in environment 1 like this:
	47	.P1 2
	48	^de NP
	49	^ev 1 \e" shift to new environment
	50	^lt 6i \e" set parameters here
	51	^ft R
	52	^ps 10
	53	\&... any other processing ...
	54	^ev \e" return to previous environment
	55	^^
	56	.P2
	57	It is also possible to initialize the parameters for an environment
	58	outside the
	59	.BD .NP
	60	macro,
	61	but the version shown keeps all the processing in one place
	62	and is thus easier to understand and change.