From e0c6872cf40896c7be36b11dcc744620f10adf1d Mon Sep 17 00:00:00 2001
From: Norbert Preining <norbert@preining.info>
Date: Mon, 2 Sep 2019 13:46:59 +0900
Subject: Initial commit

---
 info/impatient/tips.tex | 1011 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 1011 insertions(+)
 create mode 100644 info/impatient/tips.tex

(limited to 'info/impatient/tips.tex')

diff --git a/info/impatient/tips.tex b/info/impatient/tips.tex
new file mode 100644
index 0000000000..3d0f1b8b97
--- /dev/null
+++ b/info/impatient/tips.tex
@@ -0,0 +1,1011 @@
+% This is part of the book TeX for the Impatient.
+% Copyright (C) 2003, 2014 Paul W. Abrahams, Kathryn A. Hargreaves, Karl Berry.
+% See file fdl.tex for copying conditions.
+
+\input macros
+\chapter{Tips and techniques}
+
+\chapterdef{tips}
+
+\TeX\ is a complex program that occasionally works its will in
+mysterious ways.  In this section we offer some tips on solving
+problems that you might encounter and explain some handy techniques.
+
+
+\section  Correcting bad page breaks
+
+\bix^^{page breaks//bad}
+Sometimes \TeX\ breaks a page right in the middle of material that you
+want to keep together---for example,
+a section heading and the text that follows it,
+or a short list of related items.  There are two ways to correct the
+situation:
+\ulist\compact
+\li You can force the material to be kept together.
+\li You can force a page break at a different place.
+\endulist
+
+The simplest way to force \TeX\ to keep material together on a page is
+to enclose the material in a vbox using the |\vbox| command \ctsref{\vbox}.
+^^|\vbox//fixing page breaks with|
+A vbox is ordinarily better than an hbox for this purpose because most
+often the material to be kept together,
+e.g., a sequence of paragraphs, will be vertical mode material.
+You should
+precede and follow the vbox by an implicit or explicit paragraph command
+(either a blank line or |\par|); otherwise 
+\TeX\ may try to make the vbox part of an an adjacent paragraph.
+The vbox method has an important limitation:
+you can't apply it to portions of text smaller than a paragraph.
+
+You can sometimes keep the lines of a single paragraph together by enclosing
+the paragraph in a group and assigning |\interlinepenalty|
+\ctsref{\interlinepenalty} 
+a value of $10000$ at the start of the group (or elsewhere before the
+end of the paragraph).
+This method causes \TeX\ to consider page breaks within that paragraph to be
+infinitely undesirable.
+However, if all the page breaks that \TeX\ can find are infinitely undesirable,
+it may break the page within the paragraph anyway.
+
+A ^|\nobreak| command  (\xref{vnobreak})
+after the end of a paragraph prevents \TeX\
+from breaking the page at the following item
+(unless that item happens to be a penalty of less than $10000$).
+This is also the best way to prevent a page break after a heading,
+since a heading usually behaves like a paragraph.
+The |\nobreak| must follow the blank line or |\par| that ends
+the paragraph so that \TeX\ won't treat the |\nobreak| as part of the
+paragraph.
+For the |\nobreak| to be effective, it must also come before
+any legal breakpoint at the end of the paragraph.
+The glue that \TeX\ inserts
+before the next paragraph is such a breakpoint,
+and so is any vertical glue that you insert explicitly after a paragraph.
+Thus the |\nobreak| should usually be
+the very first thing after the end of the paragraph or heading.
+
+You can use the ^|\eject| command \ctsref{\eject}
+to force \TeX\ to break a page at a
+particular place.  Within a paragraph, you can use the combination 
+`|\vadjust{\vfill\eject}|' 
+\ctsref{\vadjust}
+^^|\vadjust|
+to force a break after the next complete output line.
+The reason for preceding |\eject| by ^|\vfill| 
+\ctsref{\vfill} is to
+get \TeX\ to fill out the page with blank space.  
+However, using |\eject| to fix page break problems
+has a major disadvantage:
+if the page boundaries in your document change,
+the page breaks that you've inserted may no longer be where you want them.
+
+If you don't provide \TeX\ with a |\vfill| command to fill out the page
+before an |\eject|,
+\TeX\ redistributes the extra blank space as best it can and then usually
+complains that ``an
+underfull |\vbox| (badness $10000$) has occurred while |\output| is active.''
+You may encounter a similar problem with
+any of the methods mentioned above for enclosing
+material that you want to keep together.
+
+The ^|\filbreak| command \ctsref\filbreak{}
+\xrdef{filbreak}
+provides a way of keeping the lines of one or more paragraphs
+(or other vertical mode material) together on
+a page.  If you enclose a paragraph in |\filbreak|s, \TeX\ will effectively
+ignore the |\filbreak|s if the paragraph fits on the current page and
+break the page before the first |\filbreak| if the paragraph doesn't fit.
+If you put |\filbreak|s around each paragraph in a sequence of paragraphs,
+like this:
+{\obeylines\display{
+{\tt \\filbreak}
+\<paragraph>
+{\tt \\filbreak}
+\<paragraph>
+{\tt \\filbreak}
+\leavevmode\indent\vdots
+\<paragraph>
+{\tt \\filbreak}
+}}
+\vfil\eject
+\noindent
+\TeX\ will keep the lines of each paragraph together on a page.
+If \TeX{} breaks a page at a |\filbreak|, it will fill the bottom of the
+page with blank space.
+
+Sometimes you can get \TeX\ to modify the length of a page by changing
+the ^|\looseness| parameter \ctsref\looseness{} for one or more paragraphs.
+Setting |\looseness| negative within a paragraph causes \TeX\ to try to squeeze
+the paragraph into fewer lines; setting it positive causes \TeX\ to try to
+expand the paragraph into more lines.  The disadvantage of changing |\looseness|
+is that the interword spacing in the affected region won't be optimal.
+You can get further information about \TeX's attempted line breaks by
+setting |\tracingpages| (\xref\tracingpages) to $1$.
+
+
+\section Preserving the end of a page
+
+Sometimes you need to modify something on a single page and you want to avoid
+reprinting the entire document.  If your modification doesn't 
+change the page length too much, there's hope.  You need to fix the end
+of the page so that it falls in the same place;
+the methods are similar to the ones for fixing a bad page break.
+
+If the original end of page came between paragraphs, you can
+force a page break at the same place
+using any of the methods we've described above.  Otherwise,
+you must force \emph{both} a line break and a page break at a particular
+place.  If the new page is shorter than the old one, the sequence:
+\csdisplay
+\vadjust{\vfill\eject}\break
+|
+^^|\vadjust|
+should do the trick.
+But if the new page is longer,
+the problem is far more difficult because \TeX\ has probably already
+squeezed the page as tightly as it can.  Your only hopes in this case are
+to set ^|\looseness| \ctsref\looseness{} to a negative value,
+to shorten some of the vertical skips on the page, to add some shrink to
+^|\parskip| (\xref\parskip) if it was nonzero, or, as a last resort,
+to decrease |\baselineskip| \ctsref{\baselineskip} ever so slightly.
+^^|\baselineskip//and preserving end of page|
+
+\section Leaving space at the top of a page
+
+\null
+^^{vertical space//reserving at top of page}
+You can usually use the |\vskip| command \ctsref\vskip{}
+to leave vertical space on a page.
+That doesn't work at the top of a page, however, since
+\TeX\ discards glue, kerns, and penalties that occur just after a page break.
+^^{page breaks//glue at}
+Use the ^|\topglue| command \ctsref\topglue\ instead; it produces glue that
+never disappears.
+\eix^^{page breaks//bad}
+
+
+
+\section Correcting bad line breaks
+
+\null
+\bix^^{line breaks//bad}
+If \TeX\ breaks a line in the middle of material that you wanted to keep
+on a single line, there are several ways to correct the situation:
+\ulist\compact
+\li You can force a break in a nearby place with the
+|\break| command (\xref{hbreak}).
+^^|\break//correcting line breaks with|
+\li You can insert a tie (|~|) between two words
+(see \xref{@not}) to prevent a break between them.\ttidxref{~}
+\li You can tell \TeX\ about hyphenations that it wouldn't 
+otherwise consider by
+inserting one or more discretionary hyphens in various words
+(see |\-|, \xref{\@minus}).
+\ctsidxref{-//in line breaking}
+^^{discretionary hyphens//bad line breaks, correcting with}
+\li You can enclose several words in an hbox using the ^|\hbox|
+command \ctsref{\hbox}.
+\endulist
+
+The disadvantage of all of these methods, except for inserting discretionary
+hyphens, is that they may make it impossible for \TeX\ to find a
+satisfactory set of line breaks.  Should that happen, \TeX\ will
+set one or more underfull or overfull boxes and complain about it.
+^^{underfull boxes} ^^{overfull boxes}
+The hbox method has a further disadvantage: because \TeX\ sets an hbox
+as a single unit without considering its context, the interword space 
+within the hbox may not be consistent with the interword space in the rest of
+the line.
+\eix^^{line breaks//bad}
+
+
+\section Correcting overfull or underfull boxes
+
+\null
+\bix^^{overfull boxes}
+\bix^^{underfull boxes}
+\bix^^{boxes//overfull}
+\bix^^{boxes//underfull}
+If \TeX\ complains about an overfull box, it means you've put
+more material into a box than that box has room for.  
+Similarly, if \TeX\ complains about an underfull box, it means you
+haven't put enough material into the box.  You can encounter
+these complaints under many different circumstances, so let's look at the more
+common ones:
+
+\ulist
+\li An overfull hbox that's a line of a paragraph indicates that the line was
+too long and that 
+\TeX\ couldn't rearrange the paragraph
+to make the line shorter.  If you set ^|\emergencystretch|
+\ctsref{\emergencystretch} to some nonzero
+value, that may cure the problem by allowing \TeX\ to put more space between
+words.  Another solution is to set |\tolerance| \ctsref{\tolerance}
+to $10000$, but that's likely
+to yield lines with far too much space in them.  Yet another solution is to
+insert a discretionary hyphen
+^^{discretionary hyphens//overfull boxes, correcting with}
+in a critical word that \TeX\ didn't know how to hyphenate.
+If all else fails, you might try rewording the paragraph.
+A solution that is rarely satisfactory is increasing ^|\hfuzz| \ctsref\hfuzz,
+allowing \TeX\ to construct lines that project beyond the right margin.
+
+\li An underfull hbox that's a line of a paragraph indicates that the line was
+too short and that \TeX\ couldn't rearrange the paragraph to
+make the line longer.
+\TeX\ will set such a line by stretching its interword spaces
+beyond their normal
+limits.  Two of the cures for overfull lines mentioned above
+also apply to underfull lines:
+inserting discretionary hyphens and rewording the paragraph.
+Underfull lines
+won't trouble you if you're using ragged right formatting, which you can get
+with the ^|\raggedright| command \ctsref\raggedright.
+
+\li The complaint:
+\csdisplay
+Underfull \vbox (badness 10000) has occurred
+   while \output is active
+|
+indicates that \TeX\ didn't have enough material to fill up a page.  The
+likely cause is that you've been using vboxes to keep material together
+and \TeX\ has encountered a vbox near the bottom of a page that wouldn't fit on
+that page.
+It has put the vbox on the next page, but in doing so has left too much
+empty space in the current page.
+In this case you'll either have to insert some more space
+elsewhere on the current page or break up the vbox into smaller parts.
+
+Another possible cause of this complaint is having a long paragraph
+that occupies an entire page without a break.
+Since \TeX\ won't ordinarily vary the spacing between lines,
+it may be unable to fill a gap at the bottom of the page
+amounting to a fraction of the line spacing.
+This can happen if |\vsize| \ctsref{\vsize}, the page length,
+is not an even multiple of |\baselineskip| \ctsref{\baselineskip},
+the space between consecutive
+baselines.
+
+Yet another cause of this complaint,
+similar to the previous one, is setting ^|\parskip| \ctsref{\parskip},
+the interparagraph glue, to a value that doesn't have any
+stretch or shrink. You can fix these last two problems by increasing ^|\vfuzz|
+\ctsref\vfuzz.
+
+\li The complaint
+\csdisplay
+Overfull \vbox (296.30745pt too high) has occurred
+   while \output is active
+|
+indicates that you constructed a vbox that was longer than the page.  You'll
+just have to make it shorter.
+
+\li 
+\bix^^|\hbox//overfull box from|
+\bix^^|\vbox//overfull box from|
+The only cures for an overfull hbox or vbox that you've constructed
+with the |\hbox| or |\vbox| commands
+(\pp\xrefn\hbox, \xrefn\vbox)
+are to take something out of the box, to insert some negative glue
+with ^|\hss| or ^|\vss| (\xref\hss), or to increase the size
+of the box.
+
+\li If you encounter an underfull hbox or vbox that you've constructed 
+with |\hbox| or |\vbox|,
+you're usually best off to fill out the box with ^|\hfil| 
+or ^|\vfil| (\xref\hfil).
+\eix^^|\hbox//overfull box from|
+\eix^^|\vbox//overfull box from|
+
+\endulist
+\eix^^{boxes//overfull}
+\eix^^{boxes//underfull}
+\eix^^{overfull boxes}
+\eix^^{underfull boxes}
+
+
+\section Recovering lost interword spaces
+
+\null
+^^{space//lost}
+^^{words run together}
+If you find that \TeX\ has run two words together, the likely cause is a
+control sequence that's absorbed the spaces after it.  
+Put a ^{control space} (|\!visiblespace|) after the control
+sequence.
+
+
+\section Avoiding unwanted interword spaces
+
+\null
+\bix^^{space//unwanted}\xrdef{unwantedspace}
+If you get a space in your document where you don't want and don't
+expect one, the most likely cause, in our experience,
+is an end of line or a space following a brace.
+^^{braces//space after}
+(If you're doing fancy things with category codes,
+^^{category codes//cause of unwanted spaces}
+you've introduced lots of other likely causes.)
+\TeX\ ordinarily translates an end-of-line into a space,
+and it considers a space after a right or left brace to be significant.
+
+If the unwanted space is caused by a space after a brace within
+an input line, then remove that space.
+If the unwanted space is caused by a brace at the end of an input line,
+put a `|%|' immediately after the brace.
+{\recat!ttidxref[%//to eliminate unwanted spaces]]
+The `|%|' starts a comment, but this comment needn't
+have any text.
+
+A macro definition can also
+introduce unwanted spaces if you haven't written it
+carefully.  If you're getting unwanted spaces when you call a macro, check
+its definition to be sure that you don't have an unintended space after a
+brace and that you haven't ended a line of the definition immediately
+after a brace.
+People often end lines of macro definitions after braces in order to make
+the definitions more readable.
+To be safe, put a `|%|' after any brace that ends a line of a macro
+definition.
+It may not be needed, but it won't do any harm.\footnote{
+Admittedly there are rare cases where you really do want an end of line
+after a brace.}
+
+When you're having trouble locating the source of an unwanted space,
+try setting |\tracingcommands| \ctsref{\tracingcommands} to $2$.
+You'll get a |{blank space}| command in the log file for each space
+that \TeX\ sees.
+
+It helps to know \TeX's rules for spaces:
+
+\olist
+\li Spaces are ignored at the beginnings of input lines.
+\li Spaces at the ends of input lines are ignored under \emph{all}
+circumstances, although the end of line itself is treated like a space.
+(A completely blank line, however, generates a |\par| token.)
+\li Multiple spaces are treated like a single space, but
+only if they appear together in your input.
+Thus a space following the arguments of a macro call is not combined
+with a final space produced by the macro call.  Instead, you get two spaces.
+\li Spaces are ignored after control words.
+\li Spaces are in effect ignored after numbers, dimensions,
+and the `|plus|' and `|minus|' in glue specifications.%
+\footnote{Actually, \TeX\ ignores only a
+single space in these places.
+Since multiple spaces ordinarily reduce to a single space, however, the
+effect is that of ignoring any number of spaces.}
+\endolist
+\noindent If you've changed the category code of the space or the end-of-line
+character, all bets are off.
+\eix^^{space//unwanted}
+
+
+\section Avoiding excess space around a display
+
+\null
+^^{math display}
+If you're getting too much space above a math display, it may be because
+you've left a blank line in your input above the display.
+The blank line starts a new paragraph and puts \TeX\ into 
+vertical mode.  When
+\TeX\ sees a `|$|' in vertical mode, it switches back to horizontal mode
+and inserts the interparagraph glue (|\parskip|) followed by
+the interline glue (|\baselineskip|).
+Then, when it starts the display itself,
+it inserts \emph{more} glue (either ^|\abovedisplayskip|
+or ^|\abovedisplayshortskip|, depending on the length of the preceding
+line).  
+This last glue is the only glue that you want.
+To avoid getting the interparagraph glue as well, don't leave a blank line above a
+math display or otherwise
+end a paragraph (with |\par|, say) just before a math display.
+
+Similarly,
+if you're getting too much space below a math display, it may be because
+you've left a blank line in your input below the display.
+Just remove it.
+
+
+\section Avoiding excess space after a paragraph
+
+If you get too much vertical space after a paragraph that was produced by a
+macro, you may be getting the interparagraph glue produced by the macro,
+an empty paragraph, and then more interparagraph glue.
+You can get rid of the second paragraph skip by inserting:
+\csdisplay
+\vskip -\parskip
+\vskip -\baselineskip
+|
+just after the macro call.
+If you always get this problem with a certain macro, you can put these
+lines at the end of the macro definition instead.
+You may also be able to cure the problem by never leaving a blank line
+after the macro call---if you want a blank line just to make your input
+more readable, start it with a `|%|'.
+
+
+\section Changing the paragraph shape
+
+\null
+\bix^^{paragraphs//shaping}
+Several \TeX\ parameters---^|\hangindent|, ^|\leftskip|, etc.---%
+affect the way that \TeX\ shapes paragraphs and breaks them into lines.
+^^{line breaking}
+These parameters are used indirectly in \plainTeX{} commands such as
+^|\narrower| and ^|\hang|; you can also assign to them directly.
+If you've used one of these commands (or changed one of these parameters),
+but the command or parameter change
+does not seem to be having any effect on a paragraph,
+the problem may be that you've ended a group before you've ended the
+paragraph.  For example:
+\csdisplay
+{\narrower She very soon came to an open field, with
+a wood on the other side of it: it looked much darker
+than the last wood, and Alice felt a little timid
+about going into it.}
+|
+This paragraph won't be set narrower because the right brace at the end
+terminates the |\narrower| group before \TeX\ has had a chance to
+break the paragraph into lines.  Instead, put a |\par| before the
+right brace; then you'll get the effect you want.
+^^|\par//when changing paragraph shape|
+\eix^^{paragraphs//shaping}
+
+
+\section Putting paragraphs into a box
+
+Suppose you have a few paragraphs of text that you want to put in a
+particular place on the page.  The obvious way to do it is to enclose
+the paragraphs in an hbox of an appropriate size, and then place the hbox
+where you want it to be.  Alas, the obvious way doesn't work because
+\TeX\ won't do line breaking in restricted horizontal mode.
+^^{restricted mode//horizontal}
+If you try it,
+you'll get a misleading error message that suggests you're
+missing the end of a group.
+The way around this restriction is to write:
+\csdisplay
+\vbox{\hsize = !<dimen> !dots !<paragraphs> !dots}
+|
+where \<dimen> is the line length that you want for the paragraphs.
+This is what you need to do, in particular, when you want to enclose some
+paragraphs in a box (a box enclosed in ruled lines, not a \TeX\ box).
+
+\section Drawing lines
+
+\null
+\bix^^{rules}
+You can use the ^|\hrule| and ^|\vrule| commands (\xref\hrule)
+to draw lines, i.e., rules.  You'll need to
+know (a)~where you can use each command and
+(b)~how \TeX\ determines the lengths of rules when
+you haven't given the lengths explicitly.
+\ulist
+\li You can only use |\hrule| when \TeX\ is in a vertical mode and |\vrule|
+when \TeX\ is in a horizontal mode.
+This requirement means that 
+you can't put a horizontal rule into an hbox or a vertical rule
+into a vbox.
+You can, however, construct a horizontal rule that looks vertical by
+specifying all three dimensions and making it tall and skinny.
+Similarly, you can construct a vertical rule that looks horizontal
+by making it short and fat.
+
+\li A horizontal rule inside a vbox
+has the same width as does the vbox if you haven't
+given the width of the rule explicitly.
+Vertical rules
+inside hboxes behave analogously.
+If your rules are coming out too long or too short,
+check the dimensions of the enclosing box.
+\endulist
+
+As an example, suppose we want to produce:
+\display{%
+\hbox{\vrule
+   \vbox{\hrule\vskip 3pt
+      \hbox{\hskip 3pt
+          \vbox{\hsize .7in\raggedright
+             \noindent Help! Let me out of here!}%
+      \hskip 3pt}
+   \vskip 3pt\hrule}%
+\vrule}}
+The following input will do it:
+\csdisplay
+\hbox{\vrule
+   \vbox{\hrule \vskip 3pt
+      \hbox{\hskip 3pt
+          \vbox{\hsize = .7in \raggedright
+             \noindent Help!! Let me out of here!!}%
+      \hskip 3pt}%
+   \vskip 3pt \hrule}%
+\vrule}
+|
+We need to put the text into a vbox in order to get \TeX\ to process it
+as a paragraph.
+The four levels of boxing are really
+necessary---if you doubt it, try to run this example with fewer levels.
+\eix^^{rules}
+
+
+\section Creating multiline headers or footers
+
+\null
+\xrdef{bighead}
+\bix^^{headers//multiple-line}
+\bix^^{footers//multiple-line}
+You can use
+the ^|\headline|  and ^|\footline| commands
+(\xref\footline) to produce headers and footers, but they don't work properly
+for headers and footers having more than one line.  However, you can get 
+multiline headers and footers by redefining some of the subsidiary
+macros in \TeX's output routine.
+
+For a multiline header, you need to do three things:
+\olist\compact
+\li Redefine the ^|\makeheadline| macro that's called from \TeX's
+output routine.
+\li Increase ^|\voffset| by the amount of vertical space consumed by the
+extra lines.
+\li Decrease ^|\vsize| by the same amount.
+\endolist
+\noindent The following example shows how you might do this:
+\csdisplay
+\advance\voffset by 2\baselineskip
+\advance\vsize by -2\baselineskip
+\def\makeheadline{\vbox to 0pt{\vss\noindent
+   Header line 1\hfil Page \folio\break
+   Header line 2\hfil\break
+   Header line 3\hfil}%
+   \vskip\baselineskip}
+|
+You can usually follow the pattern of this definition quite closely, just
+substituting your own header lines and choosing an appropriate multiple
+of |\baselineskip| (one less than the number of lines in the header).
+
+For a multiline footer, the method is similar:
+\olist
+\li Redefine the ^|\makefootline| macro that's called from \TeX's
+output routine.
+\li Decrease ^|\vsize| by the amount of vertical space consumed by the
+extra lines.
+\endolist
+\noindent The following example shows how you might do this:
+\csdisplay
+\advance\vsize by -2\baselineskip
+\def\makefootline{%
+   \lineskip = 24pt
+   \vbox{\raggedright\noindent
+   Footer line 1\hfil\break
+   Footer line 2\hfil\break
+   Footer line 3\hfil}}
+|
+Again, you can usually follow the pattern of this definition quite closely.
+The value of |\lineskip| determines the amount of space between the
+baseline of the last line
+of the main text on the page and the baseline of the first line of the footer.
+\eix^^{headers//multiple-line}
+\eix^^{footers//multiple-line}
+
+
+\section Finding mismatched braces
+
+\bix^^{braces//mismatched}
+\xrdef{mismatched}
+Most times when your \TeX\ input suffers from mismatched braces, you'll
+get a diagnostic from \TeX\ fairly near the place where you actually
+made the mistake.
+But one of the most frustrating errors you can get from a \TeX\ run,
+just before \TeX\ quits, is
+the following:
+\csdisplay
+(\end occurred inside a group at level 1)
+|
+This indicates that there is an extra left brace 
+or a missing right brace somewhere
+in your document, but it gives you no hint at all
+about where the problem might be.  So how can you find it?
+
+A debugging trick we've found useful
+is to insert the following line or its equivalent
+at five or six places equally spaced within the document (and not within
+a known group):
+\csdisplay
+}% a fake ending
+|
+Let's assume the problem is an extra left brace.
+If the extra left brace
+is, say, between the third and fourth fake ending,
+you'll get error messages from the first three fake endings but not from
+the fourth one.  The reason is that \TeX\ will ignore the first three
+fake endings after complaining about them,
+but the fourth fake ending will match
+the extra left brace.
+Thus you know that the extra left brace
+is somewhere between the third and fourth
+fake ending.
+If the region of the error
+is still too large for you to find it,
+just remove the original set of fake endings and
+repeat the process within that region.
+If the problem is a missing right brace rather than an extra left brace,
+you should be able to track it down once you've found its mate.
+
+This method doesn't work under all circumstances.  In particular, it doesn't
+work if your document consists of several really large groups.  But often
+you can find some variation on this method that will lead you to that
+elusive brace.
+
+If all else fails, try shortening your input by removing 
+the last half of the file
+(after stashing away the original version first!) or inserting a
+|\bye| command in the middle.
+If the error persists, you know it's in the first half; if it goes away,
+you know it's in the second half.
+By repeating this process you'll eventually find the error.
+\eix^^{braces//mismatched}
+
+
+\section Setting dimensions
+
+\null
+\bix^^{\<dimen>}
+The simplest way to set a dimension is to specify it directly, e.g.:
+\csdisplay
+\hsize = 6in
+|
+You can also specify a dimension in terms of other dimensions or as a mixture
+of different units, but it's a little more work.  There are two ways
+to construct a dimension as such a combination:
+\olist\compact
+\li You can add a dimension to a dimension parameter or to a dimension
+register.
+For example:
+\csdisplay
+\hsize = 6in \advance\hsize by 3pc % 6in + 3pc
+|
+\li You can indicate a dimension as a multiple of a dimension 
+or glue parameter or register.
+In this case, \TeX\ converts glue to a dimension by throwing away
+the stretch and shrink.  For example:
+\csdisplay
+\parindent = .15\hsize
+\advance\vsize by -2\parskip
+|
+\endolist
+\eix^^{\<dimen>}
+
+
+\section Creating composite fonts
+
+\null
+\bix^^{fonts//composite}
+It's sometimes useful to create a ``composite font'',
+named by a control sequence $\cal F$, in which all the characters
+are taken from a font $f_1$ except for a few that are
+borrowed from another font $f_2$.
+You can then set text in the composite font by using $\cal F$ just as
+you'd use any other font identifier.
+
+You can create such a composite font by defining $\cal F$ as a macro.
+In the definition of $\cal F$, you first select font $f_1$ and then
+define control sequences that produce the borrowed characters,
+set in $f_2$.
+For example, suppose that you want to 
+create a composite font |\britrm| which has all the characters of |cmr10|
+except for the dollar sign, for which you want to borrow 
+the pound sterling symbol
+from font |cmti10|.
+The pound sterling symbol in |cmti10| happens to be in the same font position
+as the dollar sign in |cmr10|.
+Here's how to do it:
+\csdisplay
+\def\britrm{%
+   \tenrm % \tenrm names the cmr10 font
+   \def\${{\tenit\char `\$}}% \tenit names the cmti10 font.
+}
+|
+Now whenever you start the font named |\britrm|,
+|\$| will produce a pound sterling symbol.
+
+You can also get the same effect by changing the category codes
+of the characters in question to make those characters active and then
+providing a definition for the character.  For example:
+\csdisplay
+\catcode `* = \active
+\def*{{\tentt \char `\*}}
+|
+In this case the asterisk will be taken from the |\tentt| font.
+If you then type the input line:
+\csdisplay
+Debbie was the * of the show.
+|
+it will be set as:
+{\font\tentt=cmtt10%
+\catcode `* = \active
+\def*{{\tentt \char `\*}}%
+\display{Debbie was the * of the show.}}
+\noindent
+
+\eix^^{fonts//composite}
+
+
+\section Reproducing text verbatim
+
+\null
+^^{verbatim text}\xrdef{verbatim}
+Verbatim text is text that is reproduced in a typeset
+document just as it appeared in the input.
+The most common use of verbatim text is in typesetting
+computer input,
+including both computer programs and input to \TeX\ itself.
+^^{computer programs, typesetting}
+Computer input is not easy to produce verbatim for two reasons:
+\olist\compact
+\li Some characters (control symbols, escape characters, braces,
+etc.) have
+special meanings to \TeX.
+\li Ends of line and multiple spaces are translated to single spaces.
+\endolist
+\noindent
+In order to produce verbatim text, you have to cancel the special meanings
+and disable the translation.  This is best done with macros.
+
+To cancel the special meanings, you need to change the category codes
+of those characters that have special meanings.
+^^{category codes//for verbatim text}
+The following macro illustrates how you might do it:
+\csdisplay
+\chardef \other = 12
+\def\deactivate{%
+   \catcode`\\ = \other   \catcode`\{ = \other
+   \catcode`\} = \other   \catcode`\$ = \other
+   \catcode`\& = \other   \catcode`\# = \other
+   \catcode`\% = \other   \catcode`\~ = \other
+   \catcode`\^ = \other   \catcode`\_ = \other
+}
+|
+But beware! Once you've changed the category codes in this way, you've lost
+the ability to use control sequences since there's no longer an escape
+character.  You need some way of getting back to the normal mode of
+operation.  We'll explain how to do that in a moment, after considering
+the other problem: disabling the translation of spaces and ends of line.
+
+\PlainTeX\ has two commands that together nearly solve the problem:
+^|\obeyspaces| \ctsref{\obeyspaces} and ^|\obeylines| \ctsref{\obeylines}.
+The two things that they don't do are to preserve spaces at the start of
+a line
+and to preserve blank lines.
+For that you need stronger measures---which are provided by
+the ^|\obeywhitespace| macro that we are about to define.
+
+\TeX\ normally insists on collecting lines into paragraphs. One way to 
+convince it to take line boundaries literally is to turn individual lines
+into paragraphs.\footnote{%
+Another way is to turn the end of line character into a |\break|
+command and provide infinite glue at the end of each line.
+^^|\break//end of line as|
+}
+You can do this by redefining the end of line character to produce
+the |\par| control sequence.  The following three macro definitions
+show how:
+
+^^{whitespace, preserving}
+\xrdef{\obeywhitespace}
+\csdisplay
+\def\makeactive#1{\catcode`#1 = \active \ignorespaces}
+{% The group delimits the text over which ^^M is active.
+   \makeactive\^^M %
+   \gdef\obeywhitespace{%
+   % Use \gdef so the definition survives the group.
+      \makeactive\^^M %
+      \let^^M = \newline %
+      \aftergroup\removebox % Kill extra paragraph at end.
+      \obeyspaces %
+   }%
+}
+\def\newline{\par\indent}
+\def\removebox{\setbox0=\lastbox}
+
+|
+A subtle point about the definition of |\obeywhitespace| is that
+|^^M| must be made active both 
+when |\obeywhitespace| is being \emph{defined} and when
+it is being \emph{used}.
+
+In order to be able to get back to normal operation after verbatim text,
+you need to choose a character that
+appears rarely if at all in the verbatim text.  This character serves as
+a temporary escape character.
+The vertical bar (|!||) is sometimes a good choice.
+With this choice, the macros:
+\csdisplay
+\def\verbatim{\par\begingroup\deactivate\obeywhitespace
+   \catcode `\!| = 0 % Make !| the new escape character.
+}
+
+\def\endverbatim{\endgroup\endpar}
+
+\def\!|{!|}
+|
+will do the trick.  Within the verbatim text, you can use a double
+vertical bar (|!|!||) to denote a single one, and you end the verbatim text
+with |!|endverbatim|.
+
+There are many variations on this technique:
+\ulist
+\li If a programming language has keywords, you can turn 
+each keyword into a command that typesets
+that keyword in boldface.  Each keyword in the input should then be
+preceded by the temporary escape character.
+\li If you have a character (again, let's assume it's the vertical bar)
+that
+\emph{never} appears in the verbatim text, you can make it active and
+cause it to end the verbatim text.  The macro definitions then go like
+this:
+\csdisplay
+{\catcode `\!| = \active
+\gdef\verbatim{%
+   \par\begingroup\deactivate\obeywhitespace
+   \catcode `!| = \active
+   \def !|{\endgroup\par}%
+}}
+|
+\endulist
+
+The ideas presented here provide only a simple approach to typesetting
+computer programs.
+Verbatim reproduction is often not as revealing or easy to read as a version
+that uses typographical conventions to reflect the syntax
+and even the semantics of the program.
+If you'd like to pursue this subject further, we recommend the following book:
+
+\smallskip{\narrower\noindent
+Baecker, Ronald M., and Marcus, Aaron, {\sl Human Factors
+and Typography for More Readable Programs}. Reading, Mass.:
+Addison-Wesley, 1990.\par}
+
+
+\section Using outer macros
+
+\null
+^^{forbidden control sequence}^^{incomplete conditional}
+If \TeX\ complains about a ``forbidden control sequence'',
+you've probably used an outer macro in a non-outer context
+\seeconcept{outer}.
+^^{macros//outer}
+An outer macro is one whose definition is
+preceded by ^|\outer|.
+An outer macro can't be used in a macro argument, in a macro definition,
+in the preamble of an alignment, or in conditional
+text, i.e., text that will be expanded only when a conditional test
+has a particular outcome.
+^^{alignments//outer control sequence in}
+Certain macros have been defined as outer because they aren't
+intended to be used in these contexts and such a use is probably an error.
+The only ways around this problem are to redefine the
+macro or to move its use to an acceptable context.
+
+Using an outer macro in an improper context can also cause
+\TeX\ to complain about a runaway situation or an incomplete conditional.
+The problem can be hard to diagnose because the error message
+gives no hint as to what it is.
+If you get such an error message, look around for a call on an outer macro.
+You may not always know that a particular macro is outer, but the
+command `^|\show||\a|' \ctsref{\show}
+will show you the definition of |\a| and also tell you
+if |\a| is outer.
+
+
+\section Changing category codes
+
+\null
+\bix^^{category codes//changing}
+Sometimes it's useful to make local changes to the category code of a
+character in some part of your document.  For instance, you might be
+typesetting a computer program
+^^{computer programs, typesetting}
+or something else that uses normally active
+characters for special purposes.  You'd then want to deactivate those
+characters so that \TeX\ will treat them as being like any other character.
+
+If you make such a local change to the category code of a character,
+you may sometimes be dismayed to find that
+\TeX\ seems to be paying no attention whatsoever to your change.  
+Two aspects of \TeX's behavior are likely causes:
+\olist
+\li \TeX\ determines the category code of an input character
+^^{input characters}
+and attaches it to the character when it reads in the character.
+Let's say you read in a tilde (|~|) and later
+change the category code of tildes,
+but make the change
+before \TeX's stomach has actually processed that \emph{particular\/} 
+tilde \seeconcept{\anatomy}.
+\TeX\ will still respond to that
+tilde using the category code as it was before the change.  
+This difficulty typically arises 
+when the tilde is part of an argument to a macro
+and the macro itself changes the category code of tilde.
+
+\li When \TeX\ is matching a call of a macro to the definition of that macro,
+it matches not just the characters in the parameter pattern but also their
+category codes.
+^^{macros//arguments of}
+^^{macros//parameters of}
+If the category code of a pattern character isn't equal to
+the category code of the same character in the call, \TeX\ won't consider
+the characters as matching.
+This effect can produce mysterious results because it 
+\emph{looks} as though the pattern should match.
+For example, if you've defined a macro:
+\csdisplay
+\def\eurodate#1/#2/#3{#2.#1.#3}
+|
+then the slash character must have the same category code when you
+call |\eurodate| as it had when you defined |\eurodate|.
+\endolist
+If the problem arises because the troublesome character is an argument to
+a macro, then
+the usual cure is to redefine the macro as a pair
+of macros |\mstart| and |\mfinish|, where
+|\mstart| is to be called before the argument text
+and |\mfinish| is to be called after it.
+|\mstart| then sets up the category codes and |\mfinish| undoes the change,
+perhaps just by ending a group.
+\eix^^{category codes//changing}
+
+
+\section Making macro files more readable
+
+\null
+\bix^^{macros//making readable}
+You can make a file of macros more readable by 
+setting the category codes of space to $9$ (ignored
+character) and ^|\endlinechar| \ctsref{\endlinechar} to $-1$
+at the beginning of the file.
+Then you can use spaces and ends of line freely in the
+macro definitions without getting 
+unwanted spaces when you call the macros.
+The ignored characters won't generate spaces, but they'll still
+act as terminators for control sequences.
+If you really do want a space, you can still get it with the ^|\space|
+command \ctsref\space.
+
+Of course you'll need to restore the category codes of space and end of line
+to their normal values ($10$ and $5$, respectively) at the end of the file.
+You can do this either by enclosing the entire file in a group or by
+restoring the values explicitly.  If you choose to enclose the file in a group,
+then you should also set ^|\globaldefs| to $1$ so that
+all the macro definitions will be global and thus visible outside of the group.
+
+A miniature example of a macro file of this form is:
+
+\csdisplay
+\catcode `\  = 9  \endlinechar = -1
+
+\def \makeblankbox #1 #2 {
+   \hbox{\lower \dp0 \vbox{\hidehrule {#1} {#2}
+   \kern -#1 % overlap rules
+   \hbox to \wd0{\hidevrule {#1} {#2}%
+      \raise \ht0  \vbox to #1{} % vrule height
+      \lower \dp0 \vtop to #1{}  % vrule depth
+      \hfil \hidevrule {#2} {#1} }
+   \kern -#1 \hidehrule {#2} {#1} } }
+
+\def\hidehrule #1 #2 {
+   \kern -#1 \hrule height#1 depth#2 \kern -#2 }
+\def\hidevrule #1 #2 {
+   \kern -#1 {\dimen0 = #1 \advance \dimen0 by #2
+   \vrule width \dimen0 } \kern -#2 }
+
+\catcode `\  = 10  \endlinechar = `\^^M
+|
+\noindent
+Without the changed category codes,
+these macros would have to be written much more compactly, using fewer
+spaces and more `|%|'s at the ends of lines.
+\eix^^{macros//making readable}
+
+\endchapter\byebye
-- 
cgit v1.2.3

