# 8  Paper and screen

Some text you want to go only to TeX. Other text you want to go only to HTML. For such purposes, use the directives

\texonly
... for TeX only ...
\endtexonly


and

\htmlonly
... for HTML only ...
\endhtmlonly


The \texonly and \htmlonly directives are defined in the macro file tex2page.tex. Thus, you must have your document \input tex2page.tex before you can use these directives. If not, running the document through TeX will produce errors of undefinition.

If you don't want to load the macros of tex2page.tex and would yet like to distinguish between TeX-only and HTML-only text in your document, you can exploit the fact that certain TeX control sequences such as \shipout have no definition in TeX2page. Thus, the conditional

\ifx\shipout\undefined
... for HTML only ...
\else
... for TeX only ...
\fi


produces differing text in the DVI and HTML output, without the need for tex2page.tex.

\htmlonly and \texonly are more robust than using conditionals such as \ifx\shipout. If you must use the latter approach, make sure that the then'' branch constitutes the HTML-only portion. This is because any verbatim occurrence of \else, \fi, or \if... commands in the TeX-only portion (to be sure, not a common situation) may cause TeX2page to misread where the then'' branch ends and the else'' branch begins. (In general, you need to be careful with \if... nesting in TeX too [8, ch 20, p 211], not just for TeX2page.)

Note that the text inside the HTML-only portion is in TeX format. To specify some of this text as raw HTML, enclose it in \rawhtml ... \endrawhtml.

\htmlonly
... \rawhtml raw HTML text \endrawhtml ...
\endhtmlonly


The \rawhtml environment can occur only within an HTML-only text (whether described by \htmlonly or via \ifx\shipout.)

The directives are used as follows: In cases where the print and web content must differ, use \texonly and \htmlonly. In cases where the web content must use raw HTML features, use \rawhtml.

Use of these directives may seem to miss the point of TeX2page. \texonly and \htmlonly violate the principle of avoiding writing two documents, one for HTML, the other for TeX. \rawhtml violates the principle of avoiding writing raw HTML at all. \rawhtml in particular is dangerous because it voids the guarantee that the HTML output pages will be valid. Nevertheless, these directives are often useful, as the following examples show.

## 8.1  Example uses of TeX2page directives

Many TeX macros, while crucial for printed copy, are irrelevant to HTML, eg, the statement \parindent=10pt. Such macros are best enclosed in a \texonly, to avoid erroneous or fruitless translation by TeX2page.12

The \evalsto command we saw above (sec 4.1) was rather shabby. A better alternative would be to exploit TeX's math symbols, ie,

\def\evalsto{\leavevmode\hbox{$\Rightarrow$}}


or, better still (sec 6.5),

\imgdef\evalsto{\leavevmode\hbox{$\Rightarrow$}}


which avoids generating a separate image file for each use of \evalsto.

While this will work, using an image for this token is probably overkill for your HTML output. So let's make this definition TeX-only:

\texonly
\def\evalsto{\leavevmode\hbox{$\Rightarrow$}}
\endtexonly


Now, the DVI version typesets as expected, but the HTML verbatim has no access to any definition for \evalsto. In such situations, TeX2page will use the name of the command. Thus, given

\scm{
(cons 1 2) |evalsto (1 . 2)
}


the HTML output will be

(cons 1 2)  (1 . 2)


Obviously, this is no improvement over our previous \evalsto definition. While we do not want the full-fledged TeX definition, we do want some sort of poor man's equivalent'', eg,

\htmlonly
\def\evalsto{\p{=>}}
\endhtmlonly


With these definitions in place, the verbatim will now translate, in HTML, to

(cons 1 2) => (1 . 2)


While we may have relinquished TeX's niceties for our HTML version of \evalsto, we can certainly seek to compensate by using HTML's own niceties. \rawhtml comes in handy for this:

\htmlonly
\def\evalsto{\rawhtml<font
color=blue><b>=&gt;</b></font>\endrawhtml}
\endhtmlonly


The \evalsto token now has a higher contrast against the surrounding code.

(cons 1 2) => (1 . 2)


12 Actually, \parindent and other common print-specific statements are automatically recognized as irrelevant for the Web by TeX2page without the need for an explicit \texonly.