Mom -- Typesetting macros in document processing

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# USING TYPESETTING MACROS DURING DOCUMENT PROCESSING

During document processing, most of the typesetting macros affect type in the document globally. For example, if you turn kerning off, pairwise kerning is disabled not only in paragraphs, but also in headers, footers, quotes, and so on.

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.

## Top and bottom margins in document processing

Normally, mom establishes the top and bottom margins of running text in documents from the values of HEADER_MARGIN + HEADER_GAP and FOOTER_MARGIN + FOOTER_GAP respectively. However, if you invoke T_MARGIN or B_MARGIN either before or after START, they set the top and bottom margins of running text irrespective of HEADER_GAP and FOOTER_GAP.

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.

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