Typesetting macros that alter margins and line lengths affect running text globally (or at least try to), but leave headers/footers and footnotes alone. (To indent footnotes, see the full explanation of the FOOTNOTE macro.)
There are, however, some typesetting macros that, used during document processing, behave in special ways. These are the macros that deal with the basic parameters of type style: horizontal and vertical margins, line length, family, font, point size, leading, and quad.
NOTE: See the section on Top and bottom margins in document processing for information on how mom interprets T_MARGIN and B_MARGIN in document processing.
Mom assumes that any changes to these parameters stem from a temporary need to set type in a style different from that provided by mom's document element tags. In other words, you need to do a bit of creative typesetting in the middle of a document.
The following lists those typesetting macros whose behaviour during document processing requires some explanation.
MACRO EFFECT DURING DOCUMENT PROCESSING
----- ---------------------------------
L_MARGIN *The left margin of all running text
assumes the new value.
*The line length remains unaltered.
*The header and footer left margin
remain at the current document default.
(You won't use this often by itself. Most
likely, you'll use it in combination with
R_MARGIN or LL.)
R_MARGIN *The right margin of all running text
assumes the new value. In other words,
the line length is altered.
*The header and footer right margin
remain at the current document default.
LL *The line length of all running text
is set to the new value.
*The header and footer line length remain
at the current document default.
FAMILY *Changes family for the duration of the
current tag only. As soon as another document
element tag is invoked, the family reverts to
the current default for the new tag.
FT *Changes font for the duration of the
current tag only. As soon as another document
element tag is entered, the font reverts
to the current default for the new tag.
N.B. -- \*[SLANT] and \*[BOLDER] affect
paragraph text, and remain in effect for all
paragraphs until turned off. If you want to
use them in a macro that takes a string
argument, include the escape in the string.
\*[COND] and \*[EXT] behave similarly.
PT_SIZE *Changes point size for the duration of the
current tag only. As soon as another document
element tag is entered, the point size reverts
to the current document default for the new
tag.
LS *Changes line space for the duration of the
current tag only. As soon as another document
element tag is entered, the line space reverts to
the current document default for the new
tag. Highly NOT recommended, since changes to
a document's leading interfere with mom's
ability to balance bottom margins.
QUAD *Changes quad for the duration of the
current tag only. As soon as another document
element tag is entered, the quad reverts to
the current document default for the new
tag.
N.B. -- Line-for-line quadding macros
(LEFT, CENTER, RIGHT) are also temporary,
overridden by the QUAD value of any subsequent
document element tag.
Put another way, in document processing, T_MARGIN and B_MARGIN set the top and bottom margins of running text, but have no effect on the placement of headers, footers, or page numbers.