User definitions
****************

This chapter describes definitions that are meant to be used directly in a document.  When appropriate, ways to change the default formatting are described in subsections.

Diagnostics
===========

Plain TeX provides the \tracingall command, to turn on the maximum amount of tracing possible in TeX.  The (usually voluminous) output from \tracingall goes both on the terminal and into the transcript file. It is sometimes easier to have the output go only to the transcript file, so you can peruse it at your leisure and not obscure other output to the terminal.  So, Eplain provides the command \loggingall. (For some reason, this command is available in Metafont, but not in TeX.)

It is also sometimes useful to see the complete contents of boxes. \tracingboxes does this.  (It doesn't affect whether or not the contents are shown on the terminal.)

You can turn off all tracing with \tracingoff.

You can also turn logging on and off globally, so you don't have to worry about whether or not you're inside a group at the time of command. These variants are named \gloggingall and \gtracingall.

Finally, if you write your own help messages (see \newhelp in The TeXbook), you want a convenient way to break lines in them.  This is what TeX's \newlinechar parameter is for; however, plain TeX doesn't set \newlinechar.  Therefore, Eplain defines it to be the character ^^J.

For example, one of Eplain's own error messages is defined as follows:

     \newhelp\envhelp{Perhaps you forgot to end the previous^^J%
        environment? I'm finishing off the current group,^^J%
        hoping that will fix it.}%

Rules
=====

The default dimensions of rules are defined in chapter 21 of the The TeXbook.  To sum up what is given there, the ``thickness'' of rules is 0.4pt by default.  Eplain defines three parameters that let you change this dimension: \hruledefaultheight, \hruledefaultdepth, and \vruledefaultwidth.  By default, they are defined as The TeXbook describes.

But it would be wrong to redefine \hrule and \vrule.  For one thing, some macros in plain TeX depend on the default dimensions being used; for another, rules are used quite heavily, and the performance impact of making it a macro can be noticeable.  Therefore, to take advantage of the default rule parameters, you must use \ehrule and \evrule.

Citations
=========

Bibliographies are part of almost every technical document.  To handle them easily, you need two things: a program to do the tedious formatting, and a way to cite references by labels, rather than by numbers.  The BibTeX program, written by Oren Patashnik, takes care of the first item; the citation commands in LaTeX, written to be used with BibTeX, take care of the second.  Therefore, Eplain adopts the use of BibTeX, and virtually the same interface as LaTeX.

The general idea is that you put citation commands in the text of your document, and commands saying where the bibliography data is.  When you run TeX, these commands produce output on the file with the same root name as your document (by default) and the extension .aux. BibTeX reads this file.  You should put the bibliography data in a file or files with the extension .bib. BibTeX writes out a file with the same root name as your document and extension .bbl.  Eplain reads this file the next time you run your document through TeX.  (It takes multiple passes to get everything straight, because usually after seeing your bibliography typeset, you want to make changes in the .bib file, which means you have to run BibTeX again, which means you have to run TeX again...)  An annotated example of the whole process is given below.

If your document has more than one bibliography---for example, if it is a collection of papers---you can tell Eplain to use a different root name for the .bbl file by defining the control sequence \bblfilebasename. The default definition is simply \jobname.

See the document BibTeXing (whose text is in the file btxdoc.tex, which should be in the Eplain distribution you got) for information on how to write your .bib files.  Both the BibTeX and the Eplain distributions contain several examples, also.

The \cite command produces a citation in the text of your document.  The exact printed form the citation will take is under your control; see Formatting citations.  \cite takes one required argument, a comma-separated list of cross-reference labels (see Cross-references, for exactly what characters are allowed in such labels).  Warning: spaces in this list are taken as part of the following label name, which is probably not what you expect. The \cite command also produces a command in the .aux file that tells BibTeX to retrieve the given reference(s) from the .bib file.  \cite also takes one optional argument, which you specify within square brackets, as in LaTeX.  This text is simply typeset after the citations.  (See the example below.)

Eplain can create hypertext links for citations pointing to the relevant bibliography entries; see Citation hyperlinks.

Another command, \nocite, puts the given reference(s) into the bibliography, but produces nothing in the text.

The \bibliography command is next.  It serves two purposes: producing the typeset bibliography, and telling BibTeX the root names of the .bib files.  Therefore, the argument to \bibliography is a comma separated list of the .bib files (without the .bib).  Again, spaces in this list are significant.

You tell BibTeX the particular style in which you want your bibliography typeset with one more command: \bibliographystyle. The argument to this is a single filename STYLE, which tells BibTeX to look for a file STYLE.bst. See the document Designing BibTeX styles (whose text is in the btxhak.tex) for information on how to write your own styles.

Eplain automatically reads the citations from the .aux file when your job starts.

If you don't want to see the messages about undefined citations, you can say \xrefwarningfalse before making any citations. Eplain automatically does this if the .aux file does not exist. You can restore the default by saying \xrefwarningtrue.

Here is a TeX input file that illustrates the various commands.

     \input eplain                    % Reads the .aux file.
     Two citations to Knuthian works:
       \cite[note]{surreal,concrete-math}.
     \beginsection{References.}\par   % Title for the bibliography.
     \bibliography{knuth}             % Use knuth.bib for the labels.
     \bibliographystyle{plain}        % Number the references.
     \end                             % End of the document.

If we suppose that this file was named citex.tex and that the bibliography data is in knuth.bib (as the \bibliography command says), the following commands do what's required.  ($ represents the shell prompt.)

     $ tex citex       (produces undefined citation messages)
     $ bibtex citex    (read knuth.bib and citex.aux, write citex.bbl)
     $ tex citex       (read citex.bbl, still have undefined citations)
     $ tex citex       (one more time, to resolve the references)

(The texi2dvi program can help you automate this process, see Invoking Eplain.)

The output looks something like (because we used the plain bibliography style):

     Two citations to Knuthian works: [2,1 note].

     References

     [1] Ronald L. Graham, Donald E. Knuth, and Oren Patashnik.  Concrete Mathematics. Addison-Wesley, Reading, Massachusetts, 1989.

     [2] Donald E. Knuth. Surreal Numbers. Addison-Wesley, Reading, Massachusetts, 1974.

See the BibTeX documentation for information on how to write the bibliography databases, and the bibliography styles that are available. (If you want your references printed with names, as in [Knu74], instead of numbered, the bibliography style is alpha.)

Formatting citations
--------------------

You may wish to change Eplain's formatting of citations; i.e., the result of your \cite commands.  By default, the citation labels are printed one after another, separated by commas and enclosed in brackets, using the main text font.  Some formats require other styles, such as superscripted labels.  You can accomodate such formats by redefining the following macros.

\printcitestart

\printcitefinish
     Eplain expands these macros at the begining and end of the list of citations for each \cite command.  By default, they produce a [ and ], respectively.

\printbetweencitations
     If a \cite command has multiple citations, as in \cite{acp,texbook}, Eplain expands this macro in between each pair of citations.  By default, it produces a comma followed by a space.

\printcitenote
     This macro takes one argument, which is the optional note to the \cite command.  If the \cite command had no note, this macro isn't used.  Otherwise, it should print the note.  By default, the note is preceded with a comma and a space.

Here is an example, showing you could produce citations as superscripted labels, with the optional notes in parentheses.

     \def\printcitestart{\unskip $^\bgroup}
     \def\printbetweencitations{,}
     \def\printcitefinish{\egroup$}
     \def\printcitenote#1{\hbox{\sevenrm\space (#1)}}

Formatting bibliographies
-------------------------

You may wish to change Eplain's formatting of the bibliography, especially with respect to the fonts that are used.  Therefore, Eplain provides the following control sequences:

\biblabelwidth
     This control sequence represents a \dimen register, and its value is the width of the widest label in the bibliography.  Although it is unlikely you will ever want to redefine it, you might want to use it if you redefine \biblabelprint, below.

\biblabelprint
     This macro takes one argument, the label to print.  By default, the label is put in a box of width \biblabelwidth, and is followed by an enspace.  When you want to change the spacing around the labels, this is the right macro to redefine.

\biblabelcontents
     This macro also takes one argument, the label to print.  By default, the label is printed using the font \bblrm (below), and enclosed in brackets.  When you want to change the appearance of the label, but not the spacing around it, this is the right macro to redefine.

\bblrm
     The default font used for printing the bibliography.

\bblem
     The font used for printing the titles and other ``emphasized'' material.

\bblsc
     In some styles, authors' names are printed in a caps-and-small-caps font.  In those cases, this font is used.

\bblnewblock
     This is invoked between each of the parts of a bibliography entry.  The default is to leave some extra space between the parts; you could redefine it to start each part on a new line (for example).  A part is simply a main element of the entry; for example, the author is a part. (It was LaTeX that introduced the (misleading, as far as I am concerned) term `block' for this.)

\biblabelextraspace
     Bibliography entries are typeset with a hanging indentation of \biblabelwidth plus this.  The default is .5em, where the em width is taken from the \bblrm font.  If you want to change this, you should do it inside \bblhook.

\bblhook
     This is expanded before reading the .bbl file.  By default, it does nothing.  You could, for example, define it to set the bibliography fonts, or produce the heading for the references.  Two spacing parameters must be changed inside \bblhook: \parskip, which produces extra space between the items; and \biblabelextraspace, which is described above. (By the way, \hookappend won't work with \bblhook, despite the names. Just use \def.)

If you are really desperate, you can also hand-edit the .bbl file that BibTeX produces to do anything you wish.

Displays
========

By default, TeX centers displayed material.  (Displayed material is just whatever you put between $$'s---it's not necessarily mathematics.)  Many layouts would be better served if the displayed material was left-justified.  Therefore, Eplain provides the command \leftdisplays, which indents displayed material by \parindent plus \leftskip, plus \leftdisplayindent.

You can go back to centering displays with \centereddisplays. (It is usually poor typography to have both centered and left-justified displays in a single publication, though.)

\leftdisplays also changes the plain TeX commands that deal with alignments inside math displays, \displaylines, \eqalignno, and \leqalignno, to produce left-justified text.  You can still override this formatting by inserting \hfill glue, as explained in The TeXbook.

Formatting displays
-------------------

If you want some other kind of formatting, you can write a definition of your own, analogous to \leftdisplays.  You need only make sure that \leftdisplaysetup is called at the beginning of every display (presumably by invoking it in TeX's \everydisplay parameter), and to define \generaldisplay.

\leftdisplays expands the old value of \everydisplay before calling \leftdisplaysetup, so that any changes you have made to it won't be lost.  That old token list as available as the value of the token register \previouseverydisplay.

Time of day
===========

TeX provides the day, month, and year as numeric quantities (unless your TeX implementation is woefully deficient).  Eplain provides some control sequences to make them a little more friendly to humans.

\monthname produces the name of the current month, abbreviated to three letters.

\fullmonthname produces the name of the current month, unabbreviated (in English).

\timestring produces the current time, as in `1:14 p.m.'

\timestamp produces the current date and time, as in `23 Apr 64  1:14 p.m.'. (Except the spacing is slightly different.)

\today produces the current date, as in `23 April 1964'.

Lists
=====

Many documents require lists of items, either numbered or simply enumerated.  Plain TeX defines one macro to help with creating lists, \item, but that is insufficient in many cases.  Therefore, Eplain provides two pairs of commands:

\numberedlist ... \endnumberedlist

\orderedlist ... \endorderedlist
     These commands (they are synonyms) produce a list with the items numbered sequentially, starting from one.  A nested \numberedlist labels the items with lowercase letters, starting with `a'.  Another nested \numberedlist labels the items with roman numerals.  Yet more deeply nested numbered lists label items with *.

\unorderedlist ... \endunorderedlist
     This produces a list with the items labelled with small black boxes (``square bullets''). A nested \unorderedlist labels items with em-dashes.  Doubly (and deeper) nested unordered lists label items with `*'s.

The two kinds of lists can be nested within each other, as well.

In both kinds of lists, you begin an item with \li. An item may continue for several paragraphs.  Each item starts a paragraph.

You can give \li an optional argument, a cross-reference label. It's defined to be the ``marker'' for the current item.  This is useful if the list items are numbered.  You can produce the value of the label with \xrefn.  See Cross-references.

Eplain can create hypertext links for the markers produced by \xrefn pointing to the relevant list item; see List hyperlinks.

You can also say \listcompact right after \numberedlist or \unorderedlist.  The items in the list will then not have any extra space between them (see Formatting lists).  You might want to do this if the items in this particular list are short.

Here is an example:

     \numberedlist\listcompact
     \li The first item.
     \li The second item.

     The second paragraph of the second item.
     \endnumberedlist

Formatting lists
----------------

Several registers define the spacing associated with lists.  It is likely that their default values won't suit your particular layout.

\abovelistskipamount, \belowlistskipamount
     The vertical glue inserted before and after every list, respectively.

\interitemskipamount
     The vertical glue inserted before each item except the first. \listcompact resets this to zero, as mentioned above.

\listleftindent, \listrightindent
     \listrightindent is the amount of space by which the list is indented on the right; i.e., it is added to \rightskip. \listleftindent is the amount of space, relative to \parindent, by which the list is indented on the left.  Why treat the two parameters differently?  Because (a) it is more useful to make the list indentation depend on the paragraph indentation; (b) footnotes aren't formatted right if \parindent is reset to zero.

The three vertical glues are inserted by macros, and preceded by penalties: \abovelistskip does \vpenalty\abovelistpenalty and then \vskip\abovelistskip.  \belowlistskip and \interitemskip are analogous.

In addition, the macro \listmarkerspace is called to separate the item label from the item text.  This is set to \enspace by default.

If you want to change the labels on the items, you can redefine these macros: \numberedmarker or \unorderedmarker. The following registers might be useful if you do:

\numberedlistdepth, \unorderedlistdepth
     These keep track of the depth of nesting of the two kinds of lists.

\itemnumber, \itemletter
     These keep track of the number of items that have been seen in the current numbered list.  They are both integer registers.  The difference is that \itemnumber starts at one, and \itemletter starts at 97, i.e., lowercase `a'.

You can also redefine the control sequences that are used internally, if you want to do something radically different:  \beginlist is invoked to begin both kinds of lists; \printitem is invoked to print the label (and space following the label) for each item; and \endlist is invoked to end both kinds of lists.

Verbatim listing
================

It is sometimes useful to include a file verbatim in your document; for example, part of a computer program.  The \listing command is given one argument, a filename, and produces the contents of that file in your document.  \listing expands \listingfont to set the current font.  The default value of \listingfont is \tt.

You can take arbitrary actions before reading the file by defining the macro \setuplistinghook. This is expanded just before the file is input.

If you want to have line numbers on the output, you can say \let\setuplistinghook = \linenumberedlisting. The line numbers are stored in the count register \lineno while the file is being read.  You can redefine the macro \printlistinglineno to change how they are printed.

You can produce in-line verbatim text in your document with \verbatim. End the text with |endverbatim.  If you need a | in the text, double it.  If the first character of the verbatim text is a space, use | . (|  will work elsewhere in the argument, too, but isn't necessary.)

For example:

     \verbatim| ||\#%&!|endverbatim

produces  |\#%&!.

Line breaks and spaces in the verbatim text are preserved.

You can change the verbatim escape character from the default | with \verbatimescapechar CHAR; for example, this changes it to @.

     \verbatimescapechar \@

The backslash is not necessary in some cases, but is in others, depending on the catcode of the character.  The argument to \verbatimescapechar is used as \catcode `CHAR, so the exact rules follow that for \catcode.

Because \verbatim must change the category code of special characters, calling inside a macro definition of your own does not work properly.  For example:

     \def\mymacro{\verbatim &#%|endverbatim}% Doesn't work!

To accomplish this, you must change the category codes yourself before making the macro definition.  Perhaps \uncatcodespecials will help you (see Category codes).

Contents
========

Producing a table of contents that is both useful and aesthetic is one of the most difficult design problems in any work.  Naturally, Eplain does not pretend to solve the design problem.  Collecting the raw data for a table of contents, however, is much the same across documents. Eplain uses an auxiliary file with extension .toc (and the same root name as your document) to save the information.

To write an entry for the table of contents, you say \writetocentry{PART}{TEXT}, where PART is the type of part this entry is, e.g., chapter, and TEXT is the text of the title. \writetocentry puts an entry into the .toc file that looks like \tocPARTentry{TEXT}{PAGE NUMBER}.  The TEXT is written unexpanded.

A related command, \writenumberedtocentry, takes one additional argument, the first token of which is expanded at the point of the \writenumberedtocentry, but the rest of the argument is not expanded.  The usual application is when the parts of the document are numbered.  On the other hand, the one-level expansion allows you to use the argument for other things as well (author's names in a proceedings, say), and not have accents or other control sequences expanded.  The downside is that if you want full expansion of the third argument, you don't get it---you must expand it yourself, before you call \writenumberedtocentry.

For example:

     \writenumberedtocentry{chapter}{A $\sin$ wave}{\the\chapno}
     \writetocentry{section}{A section title}

Supposing \the\chapno expanded to 3 and that the \write's occurred on pages eight and nine, respectively, the above writes the following to the .toc file:

     \tocchapterentry{A $\sin$ wave}{3}{8}
     \tocsectionentry{A section title}{9}

You read the .toc file with the command \readtocfile. Naturally, whatever \toc... entry commands that were written to the file must be defined when \readtocfile is invoked.  Eplain has minimal definitions for \tocchapterentry, \tocsectionentry, and \tocsubsectionentry, just to prevent undefined control sequence errors in common cases.  They aren't suitable for anything but preliminary proofs.

Each of \writetocentry and \writenumberedtocentry opens the .toc file for writing, thereby deleting the information from the previous run.  You should therefore arrange that \readtocfile be called before the first call to a \writetoc... macro. \readtocfile does not itself delete the information from the .toc file, so that you can call it several times, e.g., to create both a short and normal table of contents.  (To produce this in particular, define \tocsectionentry to produce nothing while you are reading .toc file for a short table of contents (see Macro arguments).)

On the other hand, if you don't want to rewrite the .toc file at all, perhaps because you are only running TeX on part of your manuscript, you can set \rewritetocfilefalse.

By default, the .toc file has the root \jobname.  If your document has more than one contents---for example, if it is a collection of papers, some of which have their own contents---you can tell Eplain to use a different root name by defining the control sequence \tocfilebasename.

In addition to the usual table of contents, you may want to have a list of figures, list of tables, or other such contents-like list. You can do this with \definecontentsfile{ABBREV}.  All of the above commands are actually a special case that Eplain predefines with

     \definecontentsfile{toc}

The ABBREV is used both for the file extension and in the control sequence names.

Cross-references
================

It is often useful to refer the reader to other parts of your document; but putting literal page, section, equation, or whatever numbers in the text is certainly a bad thing.

Eplain therefore provides commands for symbolic cross-references.  It uses an auxiliary file with extension .aux (and the same root name as your document) to keep track of the information.  Therefore, it takes two passes to get the cross-references right---one to write them out, and one to read them in.  Eplain automatically reads the .aux file at the first reference; after reading it, Eplain reopens it for writing.

You can control whether or not Eplain warns you about undefined labels.  See Citations.

Labels in Eplain's cross-reference commands can use characters of category code eleven (letter), twelve (other), ten (space), three (math shift), four (alignment tab), seven (superscript), or eight (subscript). For example, (a1 $&^_ is a valid label (assuming the category codes of plain TeX), but %#\{ has no valid characters.

You can also do symbolic cross-references for bibliographic citations and list items.  See Citations, and Lists.

Eplain can create hypertext links for the cross-references; see Cross-reference hyperlinks.

Defining generic references
---------------------------

Eplain provides the command \definexref for general cross-references.  It takes three arguments: the name of the label (see section above for valid label names), the value of the label (which can be anything), and the ``class'' of the reference---whether it's a section, or theorem, or what.  For example:

     \definexref{sec-intro}{3.1}{section}

Of course, the label value is usually generated by another macro using TeX count registers or some such.

\definexref doesn't actually define LABEL; instead, it writes out the definition to the .aux file, where Eplain will read it on the next TeX run.

The CLASS argument is used by the \ref and \refs commands.  See the next section.

Using generic references
------------------------

To retrieve the value of the label defined via \definexref (see the previous section), Eplain provides the following macros:

\refn{LABEL}

\xrefn{LABEL}
     \refn and \xrefn (they are synonyms) produce the bare definition of LABEL.  If LABEL isn't defined, issue a warning, and produce LABEL itself instead, in typewriter.  (The warning isn't given if \xrefwarningfalse.)

\ref{LABEL}
     Given the class C for LABEL (see the description of \definexref in the previous section), expand the control sequence \C word (if it's defined) followed by a tie.  Then call \refn on LABEL.  (Example below.)

\refs{LABEL}
     Like \ref, but append the letter s to the \...word.

The purpose of the \...word macro is to produce the word `Section' or `Figure' or whatever that usually precedes the actual reference number.

Here is an example:

     \def\sectionword{Section}
     \definexref{sec-intro}{3.1}{section}
     \definexref{sec-next}{3.2}{section}
     See \refs{sec-intro} and \refn{sec-next} ...

This produces `See Sections 3.1 and 3.2 ...'

Page references
===============

Eplain provides two commands for handling references to page numbers, one for definition and one for use.

\xrdef{LABEL}
     Define LABEL to be the current page number.  This produces no printed output, and ignores following spaces.

\xref{LABEL}
     Produce the text `p. PAGENO', which is the usual form for cross-references.  The PAGENO is actually LABEL's definition; if LABEL isn't defined, the text of the label itself is printed.  The `p. ' prefix is defined by \xrefpageword. Its default definition is p.\thinspace.

Eplain can create hypertext links for the page references; see Page reference hyperlinks.

Equation references
===================

Instead of referring to pages, it's most useful if equation labels refer to equation numbers.  Therefore, Eplain reserves a \count register, \eqnumber, for the current equation number, and increments it at each numbered equation.

Here are the commands to define equation labels and then refer to them:

\eqdef{LABEL}
     This defines LABEL to be the current value of \eqnumber, and, if the current context is not inner, then produces a \eqno command.  (The condition makes it possible to use \eqdef in an \eqalignno construction, for example.)  The text of the equation number is produced using \eqprint.  See Formatting equation references.

     If LABEL is empty, you still get an equation number (although naturally you can't reliably refer to it).  This is useful if you want to put numbers on all equations in your document, and you don't want to think up unique labels.

     To refer to the last equation with the empty label, you just use the empty label in one of the equation reference macros (see below).  This can be handy when you want to refer to an equation shortly after its definition, say, in the sentence following the displayed equation, and do not intend to refer to the equation later.  But use this trick with extreme caution:  if later you change the text and insert another empty definition between the original definition and the reference, the reference will start to refer to the new empty-labeled equation.

\eqdefn{LABEL}
     This is like \eqdef, except it always omits the \eqno command.  It can therefore be used in places where \eqdef can't; for example, in a non-displayed equation.  The text of the equation number is not produced, so you can also use it in the (admittedly unusual) circumstance when you want to define an equation label but not print that label.

\eqref{LABEL}
     This produces a formatted reference to LABEL.  If LABEL is undefined (perhaps because it is a forward reference), it just produces the text of the label itself.  Otherwise, it calls \eqprint.

\eqrefn{LABEL}
     This produces the cross-reference text for LABEL.  That is, it is like \eqref, except it doesn't call \eqprint.

Equation labels can contain the same characters that are valid in general cross-references.

Eplain can create hypertext links for the equation references; see Equation reference hyperlinks.

Formatting equation references
------------------------------

Both defining an equation label and referring to it should usually produce output.  This output is produced with the \eqprint macro, which takes one argument, the equation number being defined or referred to.  By default, this just produces (NUMBER), where NUMBER is the equation number.  To produce the equation number in a different font, or with different surrounding symbols, or whatever, you can redefine \eqprint. For example, the following definition would print all equation numbers in italics.  (The extra braces define a group, to keep the font change from affecting surrounding text.)

     \def\eqprint#1{{\it (#1)}}

In addition to changing the formatting of equation numbers, you might to add more structure to the equation number; for example, you might want to include the chapter number, to get equation numbers like `(1.2)'.  To achieve this, you redefine \eqconstruct. For example:

     \def\eqconstruct#1{\the\chapternumber.#1}

(If you are keeping the chapter number in a count register named \chapternumber, naturally.)

The reason for having both \eqconstruct and \eqprint may not be immediately apparent.  The difference is that \eqconstruct affects the text that cross-reference label is defined to be, while \eqprint affects only what is typeset on the page.  The example just below might help.

Usually, you want equation labels to refer to equation numbers.  But sometimes you might want a more complicated text.  For example, you might have an equation `(1)', and then have a variation several pages later which you want to refer to as `(1*)'.

Therefore, Eplain allows you to give an optional argument (i.e., arbitrary text in square brackets) before the cross-reference label to \eqdef.  Then, when you refer to the equation, that text is produced. Here's how to get the example just mentioned:

     $$...\eqdef{a-eq}$$
     ...
     $$...\eqdef[\eqrefn{a-eq}*]{a-eq-var}$$
     In \eqref{a-eq-var}, we expand on \eqref{a-eq}, ...

We use \eqrefn in the cross-reference text, not \eqref, so that \eqprint is called only once.

Subequation references
----------------------

Eplain also provides for one level of substructure for equations.  That is, you might want to define a related group of equations with numbers like `2.1' and `2.2', and then be able to refer to the group as a whole: ``... in the system of equations (2)...''.

The commands to do this are \eqsubdef and \eqsubdefn. They take one LABEL argument like their counterparts above, and generally behave in the same way.  The difference is in how they construct the equation number: instead of using just \eqnumber, they also use another counter, \subeqnumber. This counter is advanced by one at every \eqsubdef or \eqsubdefn, and reset to zero at every \eqdef or \eqdefn.

You use \eqref to refer to subequations as well as main equations.

To put the two together to construct the text that the label will produce, they use a macro \eqsubreftext. This macros takes two arguments, the ``main'' equation number (which, because the equation label can be defined as arbitrary text, as described in the previous section, might be anything at all) and the ``sub'' equation number (which is always just a number).  Eplain's default definition just puts a period between them:

     \def\eqsubreftext#1#2{#1.#2}%

You can redefine \eqsubreftext to print however you like.  For example, this definition makes the labels print as `2a', `2b', and so on.

     \newcount\subref
     \def\eqsubreftext#1#2{%
       \subref = #2           % The space stops a <number>.
       \advance\subref by 96  % `a' is character code 97.
       #1\char\subref
     }

Sadly, we must define a new count register, \subref, instead of using the scratch count register \count255, because #1 might include other macro calls which use \count255.

Indexing
========

Eplain provides support for generating raw material for an index, and for typesetting a sorted index. A separate program must do the actual collection and sorting of terms, because TeX itself has no support for sorting.

Eplain can create hypertext links pointing from the index to the index terms; see Index hyperlinks.

Eplain's indexing commands were designed to work with the program MakeIndex, available from CTAN hosts in tex-archive/indexing/makeindex; MakeIndex is also commonly included in prepackaged TeX distributions.  It is beyond the scope of this manual to explain how to run MakeIndex, and all of its many options.  See http://www.ctan.org/tex-archive/indexing/makeindex/

The basic strategy for indexing works like this:

 1. For a document foo.tex, Eplain's indexing commands (e.g., \idx; see the section `Indexing terms' below) write the raw index material to foo.idx.

 2. MakeIndex reads foo.idx, collects and sorts the index, and writes the result to foo.ind.

 3. Eplain reads and typesets foo.ind on a subsequent run of TeX. See the section `Typesetting an index' below.

The texi2dvi program can help you automate this process, see Invoking Eplain.

If your document needs more than one index, each must have its own file. Therefore, Eplain provides the command \defineindex, which takes an argument that is a single letter, which replaces i in the filenames and in the indexing command names described below. For example,

     \defineindex{m}

defines the command \mdx to write to the file foo.mdx. Eplain simply does \defineindex{i} to define the default commands.

Indexing terms
--------------

Indexing commands in Eplain come in pairs: one command that only writes the index entry to the .idx file (see above section), and one that also typesets the term being indexed. The former always starts with s (for ``silent''). In either case, the name always includes Idx, where I is the index letter, also described above. Eplain defines the index i itself, so that's what we'll use in the names below.

The silent form of the commands take a subterm as a trailing optional argument.  For example, \sidx{truth}[definition of] on page 75 makes an index entry that will eventually be typeset (by default) as

     truth
       definition of, 75

Also, the silent commands ignore trailing spaces. The non-silent ones do not.

Indexing commands
.................

Here are the commands.

  * \sidx{TERM}[SUBTERM] makes an index entry for TERM, optionally with subterm SUBTERM. \idx{TERM} also produces TERM as output. Example:

          \sidx{truth}[beauty of]
          The beauty of truth is \idx{death}.

     Subterms at the second and further levels can also be specified in SUBTERM, using the \idxsubentryseparator character to separate them.  This character is by default !.

  * \sidxname{FIRST M.}{VON LAST}[SUBTERM] makes an index entry for VON LAST, FIRST M.. You can change the ,  by redefining \idxnameseparator. \idxname{FIRST M.}{VON LAST} also produces FIRST M. VON LAST as output. (These commands are useful special cases of \idx and \sidx.) Example:

          \sidxname{Richard}{Stark}
          \idxname{Donald}{Westlake} has written many kinds of novels, under
          almost as many names.

  * \sidxmarked\CS{TERM}[SUBTERM] makes an index entry for TERM[SUBTERM], but TERM will be put in the index as \CS{term}, but still sorted as just TERM.  \idxmarked\CS{TERM} also typesets \CS{term}.  This provides for the usual ways of changing the typesetting of index entries. Example:

          \def\article#1{``#1''}
          \sidxmarked\article{Miss Elsa and Aunt Sophie}
          Peter Drucker's \idxmarked\article{The Polanyis} is a remarkable
          essay about a remarkable family.

  * \sidxsubmarked{TERM}\CS{subterm} makes an index entry for TERM, SUBTERM as usual, but also puts SUBTERM in the index as \CS{term}. \idxsubmarked{TERM}\CS{subterm} also typesets TERM \CS{subterm}, in the unlikely event that your syntax is convoluted enough to make this useful. Example:

          \def\title#1{{\sl #1}}
          \sidxsubmarked{Anderson, Laurie}\title{Strange Angels}
          The \idxsubmarked{Anderson}\title{Carmen} is a strange twist.

The commands above rely on MakeIndex's feature for separating sorting of an index entry's from its typesetting. You can use this directly by specifying an index entry as SORT@TYPESET. For example:

     \sidx{Ap-weight@$A_\pi$-weight}

will sort as Ap-weight, but print with the proper math. The @ here is MakeIndex's default character for this purpose. See http://www.ctan.org/tex-archive/indexing/makeindex/. To make an index entry with an @ in it, you have to escape it with a backslash; Eplain provides no macros for doing this.

After any index command, Eplain runs \hookaction{afterindexterm}. Because the index commands always add a whatsit item to the current list, you may wish to preserve a penalty or space past the new item. For example, given a conditional \if@aftersctnhead set true when you're at a section heading, you could do:

     \hookaction{afterindexterm}{\if@aftersctnhead \nobreak \fi}

Modifying index entries
.......................

All the index commands described in the previous section take an initial optional argument before the index term, which modify the index entry's meaning in various ways.  You can specify only one of the following in any given command, except that begin and end can be specified together with pagemarkup=CS (separate them with a comma without a following space, like this: [begin,pagemarkup=defn]).

These work via MakeIndex's ``encapsulation'' feature. See Customizing indexing, if you're not using the default characters for the MakeIndex operators.  The other optional argument (specifying a subterm) is independent of these.

Here are the possibilities:

begin
end
     These mark an index entry as the beginning or end of a range. The index entries must match exactly for MakeIndex to recognize them. Example:

          \sidx[begin]{future}[Cohen, Leonard]
          ...
          \sidx[end]{future}[Cohen, Leonard]

     will typeset as something like

          future,
            Cohen, Leonard, 65--94

see
     This marks an index entry as pointing to another; the real index term is an additional (non-optional) argument to the command. Thus you can anticipate a term readers may wish to look up, yet which you have decided not to index. Example:

          \sidx[see]{analysis}[archetypal]{archetypal criticism}

     becomes

          analysis,
            archetypal, see archetypal criticism

seealso
     Similar to see (the previous item), but also allows for normal index entries of the referencing term. Example:

          \sidx[seealso]{archetypal criticism}[elements of]{dichotomies}

     becomes

          archetypal criticism,
            elements of, 75, 97, 114, see also dichotomies

     (Aside for the academically curious: The archetypally critical book I took these dichotomous examples from is Laurence Berman's The Musical Image, which I happened to co-design and typeset.)

pagemarkup=CS
     This puts \CS before the page number in the typeset index, thus allowing you to underline definitive entries, italicize examples, and the like. You do not precede the control sequence CS with a backslash. (That just leads to expansive difficulties.) Naturally it is up to you to define the control sequences you want to use. Example:

          \def\defn#1{{\sl #1}}
          \sidx[pagemarkeup=defn]{indexing}

     becomes something like

          indexing, \defn{75}

Proofing index terms
....................

As you are reading through a manuscript, it is helpful to see what terms have been indexed, so you can add others, catch miscellaneous errors, etc. (Speaking from bitter experience, I can say it is extremely error-prone to leave all indexing to the end of the writing, since it involves adding many TeX commands to the source files.)

So Eplain puts index terms in the margin of each page, if you set \indexproofingtrue. It is false by default. The terms are typeset by the macro \indexproofterm, which takes a single argument, the term to be typeset. Eplain's definition of \indexproofterm just puts it into an \hbox, first doing \indexprooffont, which Eplain defines to select the font cmtt8. With this definition long terms run off the page, but since this is just for proofreading anyway, it seems acceptable.

On the other hand, we certainly don't want the index term to run into the text of the page, so Eplain uses the right-hand side of the page rather than the left-hand page (assuming a language read left to right here). So \ifodd\pageno, Eplain kerns by \outsidemargin, otherwise by \insidemargin. If those macros are undefined, \indexsetmargins defines them to be one inch plus \hoffset.

To get the proofing index entries on the proper page, Eplain defines a new insertion class \@indexproof. To unbox any index proofing material, Eplain redefines \makeheadline to call \indexproofunbox before the original \makeheadline. Thus, if you have your own output routine, that redefines or doesn't use \makeheadline, it's up to you to call \indexproofunbox at the appropriate time.

Typesetting an index
--------------------

The command \readindexfile{i} reads and typesets the .ind file that MakeIndex outputs (from the .idx file which the indexing commands in the previous sections write).  Eplain defines a number of commands that support the default MakeIndex output.

More precisely, \readindexfile reads \indexfilebasename.INDEX-LETTERnd, where the INDEX-LETTER is the argument. \indexfilebasename is \jobname by default, but if you have different indexes in different parts of a book, you may wish to change it, just as with bibliographies (see Citations).

MakeIndex was designed to work with LaTeX; therefore, by default the .ind file starts with \begin{theindex} and ends with \end{theindex}. If no \begin has been defined, Eplain defines one to ignore its argument and set up for typesetting the index (see below), and also defines a \end to ignore its argument. (In a group, naturally, since there is a primitive \end).

Eplain calls \indexfonts, sets \parindent = 0pt, and does \doublecolumns (see Multiple columns) at the \begin{theindex}. \indexfonts does nothing by default; it's just there for you to override. (Indexes are usually typeset in smaller type than the main text.)

It ends the setup with \hookrun{beginindex}, so you can override anything you like in that hook (see Hooks). For example:

     \hookaction{beginindex}{\triplecolumns}

MakeIndex turns each main index entry into an \item, subentries into \subitem, and subsubentries into \subsubitem. By default, the first line of main entries are not indented, and subentries are indented 1em per level. Main entries are preceded by a \vskip of \aboveitemskipamount, 0pt plus2pt by default. Page breaks are encouraged before main entries (\penalty -100), but prohibited afterwards---Eplain has no provision for ``continued'' index entries.

All levels do the following:

     \hangindent = 1em
     \raggedright
     \hyphenpenalty = 10000

Each entry ends with \hookrun{indexitem}, so you can change any of this. For example, to increase the allowable rag:

     \hookaction{indexitem}{\advance\rightskip by 2em}

Finally, MakeIndex outputs \indexspace between each group of entries in the .ind file. Eplain makes this equivalent to \bigbreak.

Customizing indexing
--------------------

By default, MakeIndex outputs ,  after each term in the index. To change this, you can add the following to your MakeIndex style (.ist) file:

     delim_0 "\\afterindexterm "
     delim_1 "\\afterindexterm "
     delim_2 "\\afterindexterm "

Eplain makes \afterindexterm equivalent to \quad.

You can also change the keywords Eplain recognizes (see Modifying index entries):

\idxrangebeginword
     `begin'

\idxrangeendword
     `end'

\idxseecmdword
     `see'

\idxseealsocmdword
     `seealso'

You can also change the magic characters Eplain puts into the .idx file, in case you've changed them in the .ist file:

\idxsubentryseparator
     !

\idxencapoperator
     |

\idxbeginrangemark
     (

\idxendrangemark
     )

There is no macro for the actual (@ by default) character, because it's impossible to make it expand properly.

You can change the (imaginary) page number that ``see also'' entries sort as by redefining \idxmaxpagenum. This is 99999 by default, which is one digit too many for old versions of MakeIndex.

The words output by Eplain for ``see'' and ``see also'' index entries are defined by \indexseeword and \indexseealsowords respectively.  You can change the typeface used for these words by redefining \seevariant.  And finally, the macros \indexsee and \indexseealso actually produce the ``see ...'' entries, so you can redefine them if you want something entirely different.  If you do redefine them, make them take two parameters, the term being referenced and the \idxmaxpagenum (the latter should normally be ignored).  See the example below.

Unfortunately, it is impossible to reliably control the commas produced by MakeIndex in front of ``see ...'' entries in the .ind file, either at MakeIndex level or at Eplain level. However, the sed script named trimsee distributed with Eplain in the test directory can be used to filter out these commas from the output of MakeIndex.  For example, suppose you want the following style for your ``see ...'' entries:

     analysis,
       archetypal (see archetypal criticism)
     archetypal criticism,
       elements of, 75, 97, 114 (see also dichotomies)

You would need to redefine these macros in your TeX file:

     \def\indexsee#1#2{({\seevariant \indexseeword\/ }#1)}
     \def\indexseealso#1#2{({\seevariant \indexseealsowords\/ }#1)}

and then filter out the commas in front of the ``see ...'' entries by running the following command to produce the .ind file (assuming the name of the .idx file is myfile.idx and the trimsee script is placed in the current directory):

     prompt$ cat myfile.idx | makeindex | ./trimsee > myfile.ind

By default, trimsee uses default page list separators and default ``see ...'' command names.  If you set up MakeIndex to use different page list separator or change the names of \indexsee and \indexseealso commands, it is possible to adjust the trimsee script through its command line options, which are the following:

-i IS
     Use IS as a regular expression matching separator before ``see ...'' commands in the input (default: , \+).

-o OS
     Use OS as a separator to replace IS before ``see ...'' commands (default:  ).

-s SEE
     Use SEE as a regular expression matching ``see ...'' commands (default: \\indexsee).

-h
--help
     Print a usage message.

-v
--version
     Print version.

trimsee reads input from the standard input, and directs its output to the standard output.

Justification
=============

Eplain defines three commands to conveniently justify multiple lines of text: \flushright, \flushleft, and \center.

They all work in the same way; let's take \center as the example.  To start centering lines, you say \center inside a group; to stop, you end the group.  Between the two commands, each end-of-line in the input file also starts a new line in the output file.

The entire block of text is broken into paragraphs at blank lines, so all the TeX paragraph-shaping parameters apply in the usual way. This is convenient, but it implies something else that isn't so convenient: changes to any linespacing parameters, such as \baselineskip, will have no effect on the paragraph in which they are changed.  TeX does not handle linespacing changes within a paragraph (because it doesn't know where the line breaks are until the end of the paragraph).

The space between paragraphs is by default one blank line's worth. You can adjust this space by assigning to \blanklineskipamount; this (vertical) glue is inserted after each blank line.

Here is an example:

     {\center First line.

        Second line, with a blank line before.
     }

This produces:

First line.

Second line, with a blank line before.

You may wish to use the justification macros inside of your own macros.  Just be sure to put them in a group.  For example, here is how a title macro might be defined:

     \def\title{\begingroup\titlefont\center}
     \def\endtitle{\endgroup}

Tables
======

Eplain provides a single command, \makecolumns, to make generating one particular kind of table easier.  More ambitious macro packages might be helpful to you for more difficult applications. The files ruled.tex and TXSruled.tex, available from lifshitz.ph.utexas.edu in texis/tables, is the only one I know of.

Many tables are homogenous, i.e., all the entries are semantically the same.  The arrangement into columns is to save space on the page, not to encode different meanings.  In this kind of the table, it is useful to have the column breaks chosen automatically, so that you can add or delete entries without worrying about the column breaks.

\makecolumns takes two arguments: the number of entries in the table, and the number of columns to break them into.  As you can see from the example below, the first argument is delimited by a slash, and the second by a colon and a space (or end-of-line).  The entries for the table then follow, one per line (not including the line with the \makecolumns command itself).

\parindent defines the space to the left of the table.  \hsize defines the width of the table. So you can adjust the position of the table on the page by assignments to these parameters, probably inside a group.

You can also control the penalty at a page break before the \makecolumns by setting the parameter \abovecolumnspenalty. Usually, the table is preceded by some explanatory text.  You wouldn't want a page break to occur after the text and before the table, so Eplain sets it to 10000.  But if the table produced by \makecolumns is standing on its own, \abovecolumnspenalty should be decreased.

If you happen to give \makecolumns a smaller number of entries than you really have, some text beyond the (intended) end of the table will be incorporated into the table, probably producing an error message, or at least some strange looking entries.  And if you give \makecolumns a larger number of entries than you really have, some of the entries will be typeset as straight text, probably also looking somewhat out of place.

Here is an example:

     % Arrange 6 entries into 2 columns:
     \makecolumns 6/2: % This line doesn't have an entry.
     one
     two
     three
     four
     five
     six
     Text after the table.

This produces `one', `two', and `three' in the first column, and `four', `five', and `six' in the second.

Margins
=======

TeX's primitives describe the type area in terms of an offset from the upper left corner, and the width and height of the type.  Some people prefer to think in terms of the margins at the top, bottom, left, and right of the page, and most composition systems other than TeX conceive of the page laid out in this way.  Therefore, Eplain provides commands to directly assign and increment the margins.

\topmargin = DIMEN
\bottommargin = DIMEN
\leftmargin = DIMEN

\rightmargin = DIMEN
     These commands set the specified margin to the DIMEN given. The = and the spaces around it are optional.  The control sequences here are not TeX registers, despite appearances; therefore, commands like \showthe\topmargin will not do what you expect.

\advancetopmargin by DIMEN
\advancebottommargin by DIMEN
\advanceleftmargin by DIMEN

\advancerightmargin by DIMEN
     These commands change the specified margin by the DIMEN given.

Regardless of whether you use the assignment or the advance commands, Eplain always changes the type area in response, not the other margins. For example, when TeX starts, the left and right margins are both one inch.  If you then say \leftmargin = 2in, the right margin will remain at one inch, and the width of the lines (i.e., \hsize) will decrease by one inch.

When you use any of these commands, Eplain computes the old value of the particular margin, by how much you want to change it, and then resets the values of TeX's primitive parameters to correspond. Unfortunately, Eplain cannot compute the right or bottom margin without help: you must tell it the full width and height of the final output page.  It defines two new parameters for this:

\paperheight
     The height of the output page; default is 11truein.

\paperwidth
     The width of the output page; default is 8.5truein.

If your output page has different dimensions than this, you must reassign to these parameters, as in

     \paperheight = 11truein
     \paperwidth = 17truein

Multiple columns
================

Eplain provides for double, triple, and quadruple column output:  say \doublecolumns, \triplecolumns, or \quadcolumns, and from that point on, the manuscript will be set in columns.  To go back to one column, say \singlecolumn.

You may need to invoke \singlecolumn to balance the columns on the last page of output.

To do a ``column eject'', i.e., move to the top of the next column, do \columnfill. This does not actually force an eject, however: it merely inserts a kern of size \@normalvsize minus \pagetotal (\@normalvsize being the usual height of the page; to implement multicolumns, Eplain multiplies \vsize itself by the number of columns). In most circumstances, a column break will be forced after this kern (during the column splitting operation when the whole page is output), as desired.

The columns are separated by the value of the dimen parameter \gutter.  Default value is two picas. If you want to add vertical material between the columns, use \gutterbox. For example, to put a vertical line between columns, define \gutterbox as

     \def\gutterbox{\vbox to \dimen0{\vfil\hbox{\vrule height\dimen0}\vfil}}%

The dimension counter \dimen0 contains the height of the column.

All the \...columns macros insert the value of the glue parameter \abovecolumnskip before the multicolumn text, and the value of the glue parameter \belowcolumnskip after it.  The default value for both of these parameters is \bigskipamount, i.e., one linespace in plain TeX.

The macros take into account only the insertion classes defined by plain TeX; namely, footnotes and \topinserts.  If you have additional insertion classes, you will need to change the implementation.

Also, Eplain makes insertions the full page width. There is no provision for column-width insertions.

Footnotes
=========

The most common reference mark for footnotes is a raised number, incremented on each footnote.  The \numberedfootnote macro provides this.  It takes one argument, the footnote text.

If your document uses only numbered footnotes, you could make typing \numberedfootnote more convenient with a command such as:

     \let\footnote = \numberedfootnote

After doing this, you can type your footnotes as \footnote{FOOTNOTE TEXT}, instead of as \numberedfootnote{FOOTNOTE TEXT}.

Eplain keeps the current footnote number in the count register \footnotenumber.  So, to reset the footnote number to zero, as you might want to do at, for example, the beginning of a chapter, you could say \footnotenumber=0.

Plain TeX separates the footnote marker from the footnote text by an en space (it uses the \textindent macro).  In Eplain, you can change this space by setting the dimension register \footnotemarkseparation. The default is still an en.

You can produce a space between footenotes by setting the glue register \interfootnoteskip. The default is zero.

\parskip is also set to zero by default before the beginning of each footnote (but not for the text of the footnote).

You can also control footnote formatting in a more general way: Eplain expands the token register \everyfootnote before a footnote is typeset, but after the default values for all the parameters have been established.  For example, if you want your footnotes to be printed in seven-point type, indented by one inch, you could say:

     \everyfootnote = {\sevenrm \leftskip = 1in}

By default, an \hrule is typeset above each group of footnotes on a page.  You can control the dimensions of this rule by setting the dimension registers \footnoterulewidth and \footnoteruleheight. The space between the rule and the first footnote on the page is determined by the dimension register \belowfootnoterulespace. If you don't want any rule at all, set \footenoteruleheight=0pt, and, most likely, \belowfootnoterulespace=0pt.  The defaults for these parameters typeset the rule in the same way as plain TeX: the rule is 0.4 points high, 2 true inches wide, with 2.6 points below it.

The space above the rule and below the text on the page is controlled by the glue register \skip\footins.  The default is a plain TeX \bigskip.

Eplain can create hypertext links for the footnote marks; see Footnote hyperlinks.

Fractions
=========

Exercise 11.6 of The TeXbook describes a macro \frac for setting fractions, but \frac never made it into plain TeX. So Eplain includes it.

\frac typesets the numerator and denominator in \scriptfont0, slightly raised and lowered.  The numerator and denominator are separated by a slash.  The denominator must be enclosed in braces if it's more than one token long, but the numerator need not be.  (This is a consequence of \frac taking delimited arguments; see page 203 of The TeXbook for an explanation of delimited macro arguments.)

For example, \frac 23/{64} turns `23/64' into 23/64 (you can't see the difference in the Info file) .

Paths
=====

When you typeset long pathnames, electronic mail addresses, or other such ``computer'' names, you would like TeX to break lines at punctuation characters within the name, rather than trying to find hyphenation points within the words.  For example, it would be better to break the email address letters@alpha.gnu.ai.mit.edu at the @ or a ., rather than at the hyphenation points in letters and alpha.

If you use the \path macro to typeset the names, TeX will find these good breakpoints.  The argument to \path is delimited by any character other other than \ which does not appear in the name itself. | is often a good choice, as in:

     \path|letters@alpha.gnu.ai.mit.edu|

You can control the exact set of characters at which breakpoints will be allowed by calling \discretionaries.  This takes the same sort of delimited argument; any character in the argument will henceforth be a valid breakpoint within \path.  The default set is essentially all the punctuation characters:

     \discretionaries |~!@$%^&*()_+`-=#{}[]:";'<>,.?\/|

If for some reason you absolutely must use \ as the delimiter character for \path, you can set \specialpathdelimiterstrue.  (Other delimiter characters can still be used.)  TeX then processes the \path argument about four times more slowly.

The \path macro comes from path.sty, written by Nelson Beebe and Philip Taylor and available at http://www.ctan.org/tex-archive/macros/latex/contrib/misc/path.sty.

Logos
=====

Eplain redefines the \TeX macro of plain TeX to end with \null, so that the proper spacing is produced when \TeX is used at the end of a sentence. The other ...TeX macros listed here do this, also.

Eplain defines \AMSTeX, \BibTeX \AMSLaTeX, \LAMSTeX, \LaTeX \MF, and \SLiTeX to produce their respective logos.  (Sorry, the logos are not shown here.)  Some spelling variants of these are also supported.

All these macros come from texnames.sty, compiled by Nelson Beebe and available at http://www.ctan.org/tex-archive/info/biblio/texnames.sty.

Boxes
=====

The solid rectangle that Eplain uses as a marker in unordered lists (see Lists) is available by itself: just say \blackbox.

You can create black boxes of arbitrary size with \hrule or \vrule.

You can also get unfilled rectangles with \makeblankbox. This takes two explicit arguments: the height and depth of the rules that define the top and bottom of the rectangle.  (The two arguments are added to get the width of the left and right borders, so that the thickness of the border is the same on all four sides.)  It also uses, as implicit arguments, the dimensions of \box0 to define the dimensions of the rectangle it produces.  (The contents of \box0 are ignored.)

Here is an example.  This small raised open box is suitable for putting next to numbers in, e.g., a table of contents.

     \def\openbox{%
       \ht0 = 1.75pt \dp0 = 1.75pt \wd0 = 3.5pt
       \raise 2.75pt \makeblankbox{.2pt}{.2pt}
     }

Finally, you can put a box around arbitrary text with \boxit. This takes one argument, which must itself be a (TeX) box, and puts a printed box around it, separated by \boxitspace white space (3 points by default) on all four sides.  For example:

     \boxit{\hbox{This text is boxed.}}

The reason that the argument must be a box is that when the text is more than one line long, TeX cannot figure out the line length for itself.  Eplain does set \parindent to zero inside \boxit, since it is very unlikely you would want indentation there.  (If you do, you can always reset it yourself.)

\boxit uses \ehrule and \evrule so that you can easily adjust the thicknesses of the box rules.  See Rules.

Checking for PDF output
=======================

pdfTeX is a TeX variant that can output both .dvi and .pdf (Adobe's Portable Document Format) files (see http://www.ctan.org/tex-archive/systems/pdftex/).  You might sometimes want to know whether the target format is .pdf or .dvi.  The \ifpdf switch can be used to detect pdfTeX in PDF mode:

     \ifpdf
        This text is produced when pdfTeX is in PDF mode.
     \else
        This text is produced when pdfTeX is in DVI mode,
        or when some program other than pdfTeX is used.
     \fi

Keep in mind that \ifpdf is set based on the value of the \pdfoutput primitive of pdfTeX at the time Eplain is loaded.  If you change the value of \pdfoutput after you load Eplain, \ifpdf will not reflect the change.

Eplain defines \ifpdf by incorporating Heiko Oberdiek's ifpdf.sty, which is available at http://www.ctan.org/tex-archive/macros/latex/contrib/oberdiek/ifpdf.sty.

Loading LaTeX packages
======================

Eplain provides a limited support for loading LaTeX packages (.sty files---not .cls).  This will mostly work for packages which were designed with plain TeX compatibility in mind, which means that most LaTeX packages cannot be loaded.  The packages which are known to work are listed below (see Packages known to work).  If you discover a working package which is not in the list, please report it to the Eplain mailing list (see Introduction).

To set up a pseudo-LaTeX environment for the packages, Eplain uses miniltx.tex (http://www.ctan.org/tex-archive/macros/plain/graphics/miniltx.tex) from the LaTeX graphics collection, written by David Carlisle and Sebastian Rahtz (the collection is available at http://www.ctan.org/tex-archive/macros/latex/required/graphics/). Eplain extends miniltx.tex to provide some additional features, e.g., support for package options.

The \usepackage command
-----------------------

\usepackage loads a LaTeX package.  Its syntax is similar to that of LaTeX's \usepackage command:

     \usepackage[OPTIONS]{PACKAGES}[VERSION]

where OPTIONS is a comma-separated list of package options, PACKAGES is a comma-separated list of packages to load (without the .sty suffix), and VERSION is a package version number given as a date in the format YYYY/MM/DD.  If an older version of the package is found, a warning is issued.  If several packages are loaded within a single \usepackage command, the OPTIONS will be applied to each of the packages. As usual, parameters in square brackets are optional and can be omitted (together with the square brackets).

For example:

     \usepackage[foo,bar]{pack1,pack2}[2005/08/29]

will load packages pack1 and pack2, each with the options foo and bar, and will check that each of the packages are dated 2005/08/29 or newer.

Environment for loading packages
--------------------------------

Some packages request that certain commands are executed after all packages have been loaded.  In LaTeX, this means that the commands are executed at the beginning of the document, after the so-called preamble.  Neither plain TeX nor Eplain have any kind of preamble; therefore, Eplain requires that all packages be loaded inside a \beginpackages...\endpackages block, for example:

     \beginpackages
       \usepackage[foo,bar]{pack1}
       \usepackage{pack2}
     \endpackages

This requirement enables Eplain to execute the ``delayed'' commands at the end of the \beginpackages...\endpackages block.

For the same reason, it is advisable to specify only one such block per document, just like there is only one preamble in LaTeX.

Packages known to work
----------------------

The following table lists packages that had been tested and are known to work with Eplain, and locations where you can find manuals for these packages.  Some of the short descriptions of the packages were taken from the documentation for those packages.

autopict (2001/06/04 v1.1j Picture mode autoload file)
     http://tug.org/eplain/ltpictur.pdf

     This is the LaTeX ``picture mode'', started by \begin{picture} and ended by \end{picture} (in LaTeX, this package is not explicitly loaded since it is part of the LaTeX kernel).  It provides commands to draw simple figures inside your document without resorting to any external tools.

color (1999/02/16 v1.0i Standard LaTeX Color (DPC))
graphics (2001/07/07 v1.0n  Standard LaTeX Graphics (DPC,SPQR))
graphicx (1999/02/16 v1.0f  Enhanced LaTeX Graphics (DPC,SPQR))
     http://www.ctan.org/tex-archive/macros/latex/required/graphics/grfguide.pdf

     These packages are from the LaTeX graphics collection.  They provide commands for changing text/page colors, text rotation and scaling, and much more.

psfrag (1998/04/11 v3.04 PSfrag (MCG))
     http://www.ctan.org/tex-archive/macros/latex/contrib/psfrag/pfgguide.pdf

     PSfrag allows the user to precisely overlay Encapsulated PostScript (EPS) files with arbitrary (La)TeX constructions.  In order to accomplish this, the user places a simple text ``tag'' in the graphics file, as a ``position marker'' of sorts.  Then, using simple (La)TeX commands, the user instructs PSfrag to remove that tag from the figure, and replace it with a properly sized, aligned, and rotated (La)TeX equation.

url (2005/06/27 ver 3.2 Verb mode for urls, etc.)
     http://www.ctan.org/tex-archive/macros/latex/contrib/misc/url.sty

     This package provides a form of \verbatim that allows line breaks at certain characters or combinations of characters, accepts reconfiguration, and can usually be used in the argument to another command.  It is intended for email addresses, hypertext links, directories/paths, etc., which normally have no spaces.

     Eplain can create hypertext links with the \url command; see URL hyperlinks.

Packages known not to work
--------------------------

The following packages are known not to work with Eplain:

pict2e (2005/07/15 v0.2r Improved picture commands (HjG,RN))
     http://www.ctan.org/tex-archive/macros/latex/contrib/pict2e/

xcolor (2005/06/06 v2.03 LaTeX color extensions (UK))
     http://www.ctan.org/tex-archive/macros/latex/contrib/xcolor/