TtH: a ``TeX to HTML'' translator.

Abstract

Contents

1.  Capabilities

1.1  Plain TeX

1.1.1 Mathematics

Almost all of TeX's mathematics is supported with the exception of a few obscure symbols that are absent from the fonts normally available to browsers. Support includes, for example, in-line equations with subscripts and superscripts, display equations with built-up fractions, over accents, large delimiters, operators with limits; matrix, pmatrix, cases, [but not bordermatrix]; over/underbrace [but using a rule, not a brace].

1.1.2 Formatting and Macro Support

Font styles: it, bf, sl, uppercase, accented characters written like \"o or \'{e}. Guess the intent of font definitions [optionally, remove contruct].

Macro definitions: def, edef, xdef, but all definitions are global. Definitions with delimited arguments¹. Input of files [but not from the implicit texinputs path, see 5.4]. Newcount, number, advance and counter setting.

Centerline, beginsection, item, itemitem, obeylines; hang, hangindent, narrower [for entire paragraphs, hangafter ignored]. Headline is made into a title, footnote{}{}. Comments: removed.

Tables: halign [uses border style if the template contains vrule]. Settabs, \+.

1.2  L^AT_EX

1.2.1 Environments:

1.2.2 L^AT_EX Commands:

1.3  Special TeX usage for TtH

\epsfbox{file.[e]ps} Puts in an anchor called "Figure" linked to 
    file.[e]ps (default), or alternatively calls user-supplied script 
    to convert the [e]ps file to a gif image and optionally inline it.  
\special{html:"tags"} inserts ``tags'' into the HTML e.g. for images etc.  
\href{reference}{anchor} highlights ``anchor'' with href=``reference''.
\begin{[raw]html} ... \end{[raw]html} environment passed direct to output.
\tthdump{...} The group is omitted by TtH. Define \tthdump as a nop for TeX.
%%tth:... The rest of the comment line is passed to TtH (not TeX) for parsing.

1.4  Unsupported Commands

When TtH encounters TeX constructs that it cannot handle either because there is no HTML equivalent, or because it is not clever enough, it tries to remove the mess they would otherwise cause in the HTML code, generally giving a warning of the action if it is not sure what it is doing. The following are examples of constructs not translated.

 \magnification \magstep etc : Removes the whole construct.
 Any dimension and glue commands: removed.
 All conditionals (if else fi etc) except ifmmode: removed/ignored.
 Boxes: usually ignored (but this can sometimes cause problems).

2.  Installation

The source for TtH is flex code which is processed to produce a C program tth.c which comprises the distribution. This file is compiled by

	gcc -o tth tth.c

3.  Usage

Command line (switches can appear anywhere on the line):

 tth [switches -c -d ... ] <file.tex [>file.html] [2>err]

   -c prefix header "Content-type: text/HTML" (for direct web serving).
   -d disable delimited definitions.
   -e? epsfbox handling: -e1 convert figure to gif using user-supplied ps2gif.
       -e2 convert and include inline. -e0 (default) no conversion, just ref. 
   -f? sets the depth of grouping to which fractions are constructed built-up
    f3 (default) allows three levels built-up, f0 none, f9 lots. 
   -g don't guess an HTML equivalent for font definitions, just remove.
   -h print usage. -H or -? print more help.
   -i use italic as default math font.
   -Lfile  tells tth the base file (no extension) for LaTeX auxiliary input, 
      enables LaTeX commands (e.g. \frac) without a \documentclass line.
   -n number eqnarray environments just once (default number each line).
   -pdirectory  designate an additional directory to search for input files.
   -r output raw HTML (no preamble or postlude) for inclusion in other HTML.
   -xmakeindx  specify a non-standard makeindex command line.
   -v give verbose commentary. 

TtH is extremely fast in default mode on any reasonable hardware. Conversion of even large TeX files should be a matter of a second or two. This makes it possible to use TtH in a CGI script to output HTML directly from TeX source if desired; (stderr may then need to be redirected.)

4.  More Specific Details

4.1  Equations

Equations are translated internally into HTML3.2 as much as it allows. TtH uses HTML3.2 tables for layout of built-up fractions in display equations. It also uses the extension HTML tag <font face="symbol">, supported by Netscape and other major browsers (and part of the HTML4.0 specification) to render Greek and large delimiters etc. Untranslatable TeX math tokens are inserted verbatim.

The internal approach to equation translation is a major area where TtH departs from the philosophy of Latex2html and its derivatives. TtH does not use any images to try to represent hard-to-translate constructs like equations. Instead it uses the native ability of HTML to the fullest in providing a semantically correct rendering of the equation. The aesthetic qualities obtained are in practice no worse on average than Latex2html's inlined images, which are generally slightly misaligned and of uncertain scaling relative to the text. Some limitations in the HTML code are inevitable, of course, but one ends up with a compact representation that can be rendered directly by the browser without the visitor having to download any additional helper code (e.g. Java equation renderer).

TtH offers an option [-i] which makes italic the default font within equations, and thus the style more TeX-like. Because of browser bugs mentioned below, this is implemented in a rather verbose HTML style, making the output of typical documents slightly longer. Browser italic font appearance is not as satisfactory as TeX's math italic, so for many documents roman looks better.

Spacing in equations is handled slightly differently by TtH than by TeX. The reason is that most browsers use fonts that will crowd the characters horizontally too close for comfort in many cases (for example: M_||/2). Also, built-up HTML equations are more spread out vertically than in TeX. Therefore TtH equations look better if spaces are added between some characters. So TtH does not remove spaces in the original TeX file between characters in equations. The author is thus able to control this detail of layout in the HTML without messing up their TeX file - since TeX will ignore any spaces inserted. Legacy TeX code that contains a lot of spurious whitespace (ignored by TeX) may, as a result, occasionally become too spread-out when translated.

4.2  Independence of [La]TeX installation and the -L switch.

Another major difference between TtH and LaTeX2HTML is that TtH does not call the latex or tex programs at all, and is not specifically dependent upon these, or indeed any other (e.g. PERL), programs being installed on the translating system. Its portability is therefore virtually universal.

Forward references in LaTeX are handled by multiple passes that write auxiliary files. TtH does only a single pass through the source. If you want TtH to use LaTeX constructs (e.g. tableofcontents, bibliographic commands, etc.) that depend on auxiliary files, then you do need to run LaTeX on the code so that these files are generated. You must also tell TtH, using the switch -Lfilename, the base file name of these auxiliary files (which is the name of the original file omitting the extension). If TtH cannot find the relevant auxiliary file because you didn't run LaTeX and generate the files or didn't include the switch, then it will omit the construct and warn you. Forward references via ref will not work if the .aux file is unavailable, but backward references will.

If you routinely use LaTeX in a way that requires auxiliary files and grow tired of always having to specify the -L switch to TtH, a simple ``l2h'' script may be useful. For example under Linux (Un*x) a script such as

tth <$1.tex >$1.html -L$1 

4.3  Indexing

When processing a LaTeX file that contains the \makeindex command in its preamble, TtH will construct an appropriately cross-hyperlinked index that will be input when the command \printindex is encountered, which must be after all the index references \index{ ... } in the document. TtH does this independently of LaTeX, but not of the subsidiary program makeindex that is normally used with LaTeX to produce the final index ``file.ind''. TtH creates its index entries in a file with extension .tid (Tth InDex). Because of makeindex program limitations, TtH currently removes all the page-number formatting that is present in the index entry (but not the reference formatting). It also uses the section reference style ``1-2'', separated by a dash, because this is the standard form that makeindex expects and it is cumbersome to change it. The actual reference is less important to the reader than the fact that TtH inserts a link to the actual place in the document indexed. When the \printindex command is encountered, TtH closes this file and runs makeindex on it, which creates by default a file with extension .ind, and then TtH reads the .ind file in as its index. Because the .ind file that TtH produces may well be incompatible with running LaTeX itself on the file, TtH deletes the .ind file that it creates (and hence one is left without such a file at the end). If, instead of creating an index file during TtH processing, one wants to use with TtH an index file already created, all that is needed is to remove the \makeindex command from the top of the latex source. Any existing .ind file will still be input by \printindex but no indexing files will be written or deleted.

If you run TtH on a file that contains both a \makeindex command and a \printindex it will overwrite your file.ind. In the unusual situation where your index, file.ind, was created laboriously by hand and cannot be recreated, you should be very careful to remove the \makeindex command from the .tex file. For safety, of course, also save a copy of your file.ind somewhere else.

The \makeindex command, if present, will also cause TtH to add a linked entry called ``Index'' to the end of any table of contents. This entry is a highly desirable feature for an HTML file, but if there is no \printindex command at the end of the document, the index will not exist, so the reference will be non-existent.

On some operating systems with file name length restrictions, the makeindex program is called makeindx. Therefore a TtH switch is provided: -xcommandline, which substitutes commandline for the default call makeindex. Therefore, -xmakeindx will switch to the correct program name on one of these limited operating systems. This switch also allows additional parameters or switches to be passed to makeindex via e.g.  -x"makeindex -s style.sty". If you don't have the makeindex program, you can't create indexes with TtH or LaTeX, except by hand.

All of the index file processing naturally requires that TtH have write permission for the directory in which the original latex file (specified by the -L switch) resides.

4.4  Graphics Inclusion: epsfbox/includegraphics

Optionally TtH can use more appropriate graphics format, possibly using a user-supplied (script or) program called ps2gif to convert the postscript file to a gif file, ``file.gif''. When the switch -e1 or -e2 is specified, if ``file.gif'' or ``file.jpg'' already exists in the same directory as implied by the reference to ``file.ps'' then no translation is done and the file found is used instead. That gif (or jpg) is then automatically either linked (-e1) or inlined (-e2) in the document. If no gif or jpg is found, ps2gif is called. A linux (un*x) ps2gif script using Ghostscript and the pbmplus utilities for this purpose is included with the distribution. A comparable batch program can be constructed to work under other operating systems or else the translation can be done by hand. Naturally you need these utility programs or their equivalent on your system to do the conversion. The calling command-line for whatever ps2gif is supplied must be of the form: ps2gif inputfile.ext outputfile.ext. The program must have permission to write the outputfile (file.gif) in the directory in which the file.ps resides.

The Latex command \includegraphics{...} does exactly the same thing. Its optional arguments are ignored. \[e]psfig{file=...} is also treated the same.

If the extension of the file initially specified is not .ps or .eps, no conversion is done but the file is referenced or in-lined as an image. In effect, then, TtH supports postscript, encapsulated postscript, gif, and jpeg, plus any future formats that become supported by common browsers. However, LaTeX does not support these other formats, so it will give an error message if it can't find a postscript file, unless you specify the bounding box, thus preventing LaTeX interrogating the file.

4.5  Various TtH limitations

Some TeX capabilities are extremely difficult or impossible to translate into HTML because of browser limitations and are best avoided if possible. Arrays or matrices in in-line equations cannot be supported because tables cannot be placed in-line in HTML. TtH output will be strangely disjointed. Likewise built-up fractions, most over- and under-accents, and indeed anything that requires specific placement on the page other than simple subscript or superscript and underline, cannot be rendered in-line in HTML, although TtH will render them well in displaystyle. These latter constructs are nevertheless commonly used in in-line TeX. TtH adopts the policy of indicating in an unambiguous and relatively intuitive way what construct is being used (as opposed to simply omitting it). For example $\hat{a}$ is rendered [^a]. The result is rarely elegant. Therefore in authoring TeX that is known to be destined for HTML translation, one should bear in mind these limitations, and use an appropriate style.

Although TtH supports a remarkably complete subset of L^AT_EX, it is not as tolerant as T_EX itself of ambiguous or confusing style. One example is $Z_\alpha{+1} = Z_\mbox{+1}$. T_EX is clever enough to decide that \alpha is the subscript on the left, but {\mbox{+1}} is the subscript on the right. TtH isn't that clever but will warn you. Put the \mbox in braces to help it. In part, the sensitivity of TtH arises from its incomplete support of the complicated primitive details of T_EX. For example, practically any T_EX that redefines character codes will break because TtH knows nothing about the concept of character codes. (If you don't know much about it either, join the vast majority of T_EX users!) Another example is that TtH expects only letters or @ in user-defined command names, not punctuation characters etc.

4.6  Delimited-parameter macros

Delimited parameter definitions are supported but the matching of parameter templates is not 100% compatible with TeX in respect of compression of space around commands, which is particularly obscure in TeX. Generally, removal of redundant whitespace in definitions (and in their usage, of course) will improve compatibility. The recognition of these definitions can be disabled using the -d switch, in which case the definitions are simply discarded.

5.  Command Handling Limitations

5.1  Macro- and Style-file inclusion

Although global macro definitions are supported by TtH, if they contain conditional or other unsupported constructs, (e.g. expandafter) it is often better to leave the definitions in a file on the texinputs path. The file will then not be found by TtH. That provides a mechanism to include the definitions when ``TeX''ing the file, but not when ``TtH''ing it. If the definition is required in TtH, the full path should be specified relative to the directory from which TtH is run, e.g. ``\input /home/myhome/mytexdir/mymacro.tex''.

5.2  Layout to include arguments of unknown commands

Unrecognized or undefined commands of the form \dothis{one}{two}{three}, are treated by discarding all the following adjacent brace groups. A space between the close and open braces will terminate the discarded arguments and cause the following brace group(s) to be scanned as if just the text. This makes it possible to use formatting to make TeX code come out right in both TeX and HTML. For example if TtH encounters a command written ``\boxthis{width} {boxed material}'' which might be designed in TeX to provide a width to a defined command, written with a space after the first argument, it will ignore the width and scan the boxed material into the text.

5.3  Restrictions on renaming of internal commands

Since TtH supports command definition using \def or \newcommand, it will accommodate many personal macros. Currently the mechanism for interpreting defined macros does not permit a TeX construct that TtH considers to be built-in to be split between a definition and following text. For example, one might unnecessarily define a command for making text italic by putting

\def\unnecessary{\textit}

\def\unnecessary#1{\textit{#1}}

Another important factor is that in TtH (unlike TeX) built-in commands can not normally be redefined; any redefinition will simply be ignored (except inside edef and a few other places). This prevents TtH from safely allowing use of major packages that redefine standard TeX commands. For example amsTeX redefines footnote to have just one argument, which will cause problems. This particular example is potentially a problem with LaTeX too, which also redefines footnote. TtH handles this by keeping track of whether the file is LaTeX or TeX; therefore you should not mix the two dialects in a single file even though there is no need to tell TtH explicitly which type the file is. (Besides, a mixed file will play havoc with TeX itself.)

5.4  Alternate macro inclusion when translating

Sometimes T_EX files use special macro packages designed for a specific layout of journal or conference. If such a macro package in its original form uses conditionals or other unsupported constructs, it may be inadvisable to use it. (For example, amsppt.sty which is full of unsupported constructs will certainly cause errors with TtH.) A different, simpler, version of the macro package, designed with the capabilities of TtH in mind, may readily be substituted when using TtH for translation. One way to do this is to leave the original macro or style file on the texinputs path so it is not accessed by TtH, but to prefix the alternative package for TtH. This can be done without alteration of the original T_EX files by using, for example, the following command line:

cat alternate.macros file.tex | tth >output.html

6.  Browser Problems

6.1  MacIntosh browser font problems

6.2  Netscape Composer

6.3  X font problems

Symbol fonts are not normally enabled for Netscape running under X, because of the way Netscape groups its fonts. A fix for this is to install some aliases in the fonts directories or else to add a line to your .Xdefaults file. See http://venus.pfc.mit.edu/tth/Xfonts.notes. You might want to put these notes on your site for people viewing your documents.

6.4  Printing

In Netscape 3.0 under X, for example, the printing fonts are hard coded into the browser and the font-changing commands are ignored when printing. For that reason, visitors viewing TtH documents will often not be able to print readable versions of documents with lots of mathematics. This problem could, and should, be fixed in the browsers. However, if you want your readers to be able to print a high-quality paper copy of the file, then you probably want to make available to them either the TeX source or a common page-description format such as Postscript or PDF. Since HTML documents download and display so much faster and better than these other formats on the screen, TtH's translation provides the natural medium for people to browse, but not necessarily the best medium for paper production.

6.5  Other Browser Bugs

Under Wind*ws, both Netscape (3.0) and Internet Explorer (3.02) incorrectly size or space vertically the symbol glyphs so that small gaps appear between the parts of large symbols and delimiters. This occurs only at certain font sizes (different between the two browsers!) but causes a slightly annoying degradation of the appearance.

Both Netscape and IE fail (although somewhat differently) to carry font changing commands from cell to cell of HTML3.2 tables. This means that for example boldface in equations will be lost after the first fraction or built-up construct. The -i switch mostly circumvents this bug at the cost of verbose HTML, but the browsers ought to fix it.

IE can become confused about its vertical alignment in tables, with the result that symbols float above or below the horizontal line in built-up equations. This sometimes fixes itself if you simply refresh the page!

7.  Code Critique

Known limitations are significant but mostly covered above. I would be interested to hear about bugs but only if reports are accompanied by the brief section of TeX code that causes the problem. Ungraceful failures to parse straightforward TeX code are of most interest. Aesthetic critiques (with TeX code) will be considered for future improvements. Failures on complicated macros are to be expected. It is now very difficult to crash TtH by exceeding array bounds. I would like to hear about it if you succeed in crashing TtH on code that gives no error with TeX. I would be glad to receive LaTeX2e files (emailed to hutch@pfc.mit.edu) that illustrate LaTeX bugs. But please don't send LaTeX2.09 files or files that do not conform to the latest (1994) LaTeX users' guide.

The code has been compiled and run on Linux 2.0, MSDOS, and Open VMS.

8.  License

TtH is copyright © Ian Hutchinson, 1997-8 (hutch@pfc.mit.edu).

You may freely use this software for non-commercial purposes. It may not be used for commercial purposes without an additional license. If you distribute any copies, you must include this file and these conditions must apply to the recipient. No warranty of fitness for any purpose whatever is given, intended, or implied. You use this software entirely at your own risk. If you choose to use TtH, by your actions you acknowledge that any direct or consequential damage whatever is your responsibility, not mine.

9.  Acknowledgements

Many thanks for useful discussions and input to Robert Curtis, Ken Yap, Paul Gomme, Bruce Lipschultz, Mike Fridberg, Michael Sanders, Michael Patra, Bryan Anderson, Wolfram Gloger, Ray Mines, John Murdie, David Johnson, Jonathan Barron, Michael Hirsch, Jon Nimmo, Alan Flavell, Ron Kumon, Magne Rudshaug.

A.  Appendix: Non-Standard TeX Macros

The following macro definitions, although not needed for TtH, will enable a TeX file that uses the non-standard TtH commands to be correctly parsed by Plain TeX.

\def\title#1{\bgroup\leftskip 0 pt plus1fill \rightskip 0 pt plus1fill
\pretolerance=100000 \lefthyphenmin=20 \righthyphenmin=20
\noindent
#1
\par\egroup}% Centers a possibly multi-line title.
\let\author=\title % Actually smaller font than title in LaTeX.
\input epsf     % PD package defines \epsfbox for figure inclusion
\def\href#1#2{\special{html:<a href="#1">}{#2}\special{html:</a>}}
  % Macro for http reference inclusion, per hypertex.
\def\tthdump{} % Do nothing. 

Index (showing section)

auxiliary files, 4-2

bugs, 7-0

CGI script, 3-0

charcodes, 4-5

commands

     alternative files, 5-4

     handling unsupported, 1-3

     LaTeX supported, 1-2

     redefining, 5-3

     renaming, 5-3

     unknown, 5-2

     unsupported, 1-4

compile, 2-0

conditionals, see \if

definitions

     delimited, 4-6

environments, 1-2

flex, 2-0

font

     face="symbol", 4-1

fonts, 1-1

gif, 4-4

graphics files, 4-4

\headline, 1-1

HTML

     3.2, 4-1

     4.0, 4-1

     insertion, 1-3

\if, 1-4, 5-1, 5-4

in-line equations

     arrays, 4-5

     fractions, 4-5

     overaccents, 4-5

\includegraphics, 4-4

indexing, 4-3

italic

     equation style, 4-1

jpeg, 4-4

LaTeX2HTML

     differences, 4-1, 4-2

license, 8-0

limitations, 4-5

Mac browsers, 6-1

macro files, 5-1

macros

     alternate, 5-4

     special use, 1-0

makeindex, 4-3

mathematics, 1-1

Netscape Composer, 6-2

portability, 4-2

postscript, 4-4

printing, 6-4

ps2gif, 4-4

publish

     through composer disallowed, 6-2

references

     forward, 4-2

spacing, 4-1

stderr, 3-0

stdin, 3-0

stdout, 3-0

switches

     -L, 4-2

     TtH, 3-0

symbols, 6-3

Table of Contents

     Index entry, 4-3

texinputs path, 5-1

unknown commands, see commands, unknown

vertical alignment, 6-5

X fonts, 6-3

Footnotes:

¹ Delimited definitions are not 100% TeX compatible

² See appendix for TeX macros supporting these commands