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<head><title>The "etex.src" file and its adjuncts: V2.0</title>
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<H1>The e-T<big>E</big>X format source file 
<code>"etex.src" (V2.0)</code></H1>

The primary e-TeX format source file, <code>"etex.src"</code>, is in principle
merely a wrapper for <code>"plain.tex"</code>, providing modified definitions
for some Plain TeX commands (at present, just
one:&nbsp;<code>\tracingall</code>), improving and generalising
the register allocation mechanism, and adding new commands

In so doing, we have taken the opportunity to 
(a)&nbsp;provide intrinsic support for multiple-language
typesetting (by deferring the processing of patterns and exceptions until a
rudimentary language-handling environment has been defined), 
(b)&nbsp;provide a local as well as a global register allocation mechanism, 
(c)&nbsp;provide for the allocation of blocks of registers as well as single 
	registers, 
(d)&nbsp;provide a means of allocating and accessing vectors
	(monodimensional arrays) of registers, and finally
(e)&nbsp;provide a simple but effective module-handling system, to allow e-TeX
ancilliary source files to be structured as libraries rather than as flat
linear text files. 

As the new commands and other features are not documented elsewhere,
a brief explanation of their syntax and semantics is provided here. 

<dl>
<dt><code>\tracingall</code></dt>
<dd>The definition is augmented to enable tracing for the new e-TeX
 tracing primitives <code>\tracingassigns</code>, 
 <code>\tracinggroups</code>, <code>\tracingifs</code>,
 <code>\tracingnesting</code> 
 and <code>\tracingscantokens</code>; the numeric value assigned
 to the TeX primitives <code>\tracingcommands</code> and
	<code>\tracinglostchars</code> is increased 
 as e-TeX will report additional detail in these circumstances.
 
</dd>

<dt><code>\eTeX</code></dt>
<dd>A simple implementation of the e-TeX logo; a more sophisticated version,
 capable of being used in maths sub/superscripts for example, may find
 its way into <code>etexdefs.lib</code> in due course.
 
</dd>

<dt><code>\loggingall</code></dt>
<dd>This command is equivalent to the sequence <code>\tracingall</code>
 <code>\tracingonline = 0 </code>.
 
</dd>

<dt><code>\tracingnone</code></dt>
<dd>This command restores the initial state of the various 
 <code>\tracing...</code> primitives following use of 
 <code>\tracingall</code> or <code>\loggingall</code>.
 
</dd>

<dt><code>\newmarks</code></dt>
<dd>As e-TeX provides 215 <code>\marks</code> rather than the single
 <code>\mark</code> of TeX, an allocator mechanism is required; we 
 believe that <code>\marks</code> are closer to
 <code>\box</code>es than to (say) <code>\count</code>s or
 <code>\dimen</code>s and so have provided an analogous allocation
 mechanism, in that <code>\newmarks</code>&nbsp&lt;<code>control
 sequence or active character</code>&gt; assigns a numeric
 value to the parameter rather than making it a synonym for an
 actual <code>\mark</code>; this numeric value can then be used to access
 individual <code>\marks</code>, <code>\topmarks</code>,
 <code>\splitbotmarks</code>,&nbsp;etc., as in 
<pre>
 \newmarks \rectomarks
 . . .
 \marks \rectomarks {This may form part of the recto running head}
 . . .
 \leftline {\topmarks \rectomarks}
</pre>
 It should be noted that as <code>\marks 0</code> is synonymous with
 <code>\mark</code>, <code>\newmarks</code> will never allocate that
 particular value.
 Note: 
	This command was called <code>\newmark</code> in V1.1; the alternative
	spelling has been retained for compatibility, although it is now classed
	as deprecated.
 
</dd>

<dt>
<code>\globbox</code>,
<code>\globcount</code>,
<code>\globdimen</code>,
<code>\globmarks</code>,
<code>\globmuskip</code>,
<code>\globskip</code>,
<code>\globtoks</code>
</dt>
<dd>
Analogous to TeX's <code>\newbox</code> (etc), these commands globally allocate
registers from e-TeX's extended register pool (i.e.&nbsp;from the register
range from 20 (for \marks) or from 28 
(for all other classes) to 215-1). Registers are globally 
allocated from the lower end of the range.

</dd>
<dt>
<code>\locbox</code>,
<code>\loccount</code>,
<code>\locdimen</code>,
<code>\locmarks</code>,
<code>\locmuskip</code>,
<code>\locskip</code>,
<code>\loctoks</code>
</dt>
<dd>
Analogous to <code>\globbox</code> (etc), these commands locally allocate
registers from e-TeX's extended register pool (i.e.&nbsp;from the register
range from 20 (for \marks) or from 28 
(for all other classes) to 215-1). Registers are locally
allocated from the upper end of the range.

</dd>
<dt>
<code>\globboxblk</code>,
<code>\globcountblk</code>,
<code>\globdimenblk</code>,
<code>\globmarksblk</code>,
<code>\globmuskipblk</code>,
<code>\globskipblk</code>,
<code>\globtoksblk</code>
</dt>
<dd>
These commands extend <code>\globbox</code> (etc) by globally allocating 
contiguous blocks of registers from e-TeX's extended register pool. 
The syntax used is:
<pre>
 \glob(whatever)blk &lt;control sequence or active char&gt; n
</pre>
where n specifies the length of the desired block. As
n is parsed as an undelimited parameter, it must be
expressed as a balanced text if it exceeds a single token. 
The &lt;control sequence or active character&gt; will be
<code>\mathchardef</code>'d to the ordinal of the lowest register allocated. 

</dd>
<dt>
<code>\locboxblk</code>,
<code>\loccountblk</code>,
<code>\locdimenblk</code>,
<code>\locmarksblk</code>,
<code>\locmuskipblk</code>,
<code>\locskipblk</code>,
<code>\loctoksblk</code>
</dt>
<dd>
These commands extend <code>\locbox</code> (etc) by locally allocating 
contiguous blocks of registers from e-TeX's extended register pool.
The syntax used is:
<pre>
 \loc(whatever)blk &lt;control sequence or active char&gt; n
</pre>
where n specifies the length of the desired block. As
n is parsed as an undelimited parameter, it must be
expressed as a balanced text if it exceeds a single token. 
The &lt;control sequence or active character&gt; will be
<code>\mathchardef</code>'d to the ordinal of the lowest register allocated. 

</dd>
<dt>
<code>\globcountvector</code>,
<code>\globdimenvector</code>,
<code>\globmuskipvector</code>,
<code>\globskipvector</code>,
<code>\globtoksvector</code>
</dt>
<dd>
An extension to <code>\globcountblk</code> (etc), these commands use 
e-TeX's arithmetic expression capabilities to globally allocate 
vectors of boxes (etc) from e-TeX's extended register pool. 
The syntax used is:
<pre>
 \glob(whatever)vector &lt;control sequence or active char&gt; n
</pre>
where n specifies the length of the desired block. As
n is parsed as an undelimited parameter, it must be 
expressed as a balanced text if it exceeds a single token. Once the 
vector has been defined, element m can be accessed in both left- 
and right-hand contexts as 
<pre>
 &lt;control sequence or active char&gt; m
</pre>
where 0 &lt;= m &lt; n. As with n, m
must be expressed as a balanced text if it exceeds a single token. 

</dd>
<dt>
<code>\globboxvector</code>,
<code>\globmarksvector</code>,
</dt>
<dd>
Analogous to but subtly different from the above, these commands use 
e-TeX's arithmetic expression capabilities to globally allocate 
vectors of boxes (etc) from e-TeX's extended register pool. 
The syntax used is:
<pre>
 \glob(box-or-marks)vector &lt;control sequence or active char&gt; n
</pre>
where n specifies the length of the desired block. As
n is parsed as an undelimited parameter, it must be 
expressed as a balanced text if it exceeds a single token. Once the 
vector has been defined, element m can be accessed in left-hand
contexts as 
<pre>
 &lt;box-or-marks-referencer&gt; &lt;control sequence or active char&gt; m
</pre>
and in right-hand contexts as
<pre>
 &lt;box-or-marks-dereferencer&gt; &lt;control sequence or active char&gt; m
</pre>
where 0 &lt;= m &lt; n. As with n, m
must be expressed as a balanced text if it exceeds a single token. 

The significance of <code>&lt;box-or-marks-(de)referencer&gt;</code> is that
boxes and marks are unlike other registers in that there exists a whole family
of (de)referencers, one of which must be used in order to access
the particular element required. For boxes, the sole referencer is
<code>\setbox</code>, whilst the possible dereferencers include 
<code>\box</code>, 
<code>\copy,</code>
<code>\unhbox,</code>
<code>\unvbox,</code>,
<code>\unhcopy</code> and
<code>\unvcopy</code>.
For marks, the sole referencer is 
<code>\marks</code>, whilst the possible dereferencers include
<code>\topmarks</code>,
<code>\firstmarks</code>,
<code>\botmarks</code>,
<code>\splitfirstmarks</code> and
<code>\splitbotmarks</code>.

</dd>
<dt>
<code>\loccountvector</code>,
<code>\locdimenvector</code>,
<code>\locmuskipvector</code>,
<code>\locskipvector</code>,
<code>\loctoksvector</code>
</dt>
<dd>
An extension to <code>\loccountblk</code> (etc), these commands use 
e-TeX's arithmetic expression capabilities to locally allocate 
vectors of boxes (etc) from e-TeX's extended register pool. 
The syntax used is:
<pre>
 \loc(whatever)vector &lt;control sequence or active char&gt; n
</pre>
where n specifies the length of the desired block. As
n is parsed as an undelimited parameter, it must be 
expressed as a balanced text if it exceeds a single token. Once the 
vector has been defined, element m can be accessed in both left- 
and right-hand contexts as 
<pre>
 &lt;control sequence or active char&gt; m
</pre>
where 0 &lt;= m &lt; n. As with n, m
must be expressed as a balanced text if it exceeds a single token. 

</dd>
<dt><code>\locboxvector</code>,
<code>\locmarksvector</code>,
</dt>
<dd>
Analogous to but subtly different from the above, these commands use 
e-TeX's arithmetic expression capabilities to locally allocate 
vectors of boxes (etc) from e-TeX's extended register pool. 
The syntax used is:
<pre>
 \loc(box-or-marks)vector &lt;control sequence or active char&gt; n
</pre>
where n specifies the length of the desired block. As
n is parsed as an undelimited parameter, it must be 
expressed as a balanced text if it exceeds a single token. Once the 
vector has been defined, element m can be accessed in left-hand
contexts as 
<pre>
 &lt;box-or-marks-referencer&gt; &lt;control sequence or active char&gt; m
</pre>
and in right-hand contexts as
<pre>
 &lt;box-or-marks-dereferencer&gt; &lt;control sequence or active char&gt; m
</pre>
where 0 &lt;= m &lt; n. As with n, m
must be expressed as a balanced text if it exceeds a single token. 

The significance of <code>&lt;box-or-marks-(de)referencer&gt;</code> is that
boxes and marks are unlike other registers in that there exists a whole family
of (de)referencers, one of which must be used in order to access
the particular element required. For boxes, the sole referencer is
<code>\setbox</code>, whilst the possible dereferencers include 
<code>\box</code>, 
<code>\copy,</code>
<code>\unhbox,</code>
<code>\unvbox,</code>,
<code>\unhcopy</code> and
<code>\unvcopy</code>.
For marks, the sole referencer is 
<code>\marks</code>, whilst the possible dereferencers include
<code>\topmarks</code>,
<code>\firstmarks</code>,
<code>\botmarks</code>,
<code>\splitfirstmarks</code> and
<code>\splitbotmarks</code>.

</dd>
<dt><code>\reserveinserts</code></dt>
<dd>As there are now so many registers available, there is a risk that a macro
package may allocate so many that there are none of the first 255 
left for use by insertions (which cannot use the extended register set).
<code>\reserveinserts</code> n allows a package writer or user to 
reserve an additional n insertions above and beyond those already 
allocated. The syntax used is:
<pre>
 \reserveinserts n
</pre>
n must be expressed as a balanced text if it exceeds a single token. 

</dd>

<dt><code>\load</code></dt>
<dd>Although (Plain) TeX provides facilities for either
 <code>\input</code>ting a complete file or for <code>\read</code>ing a
 file line-by-line, it makes no provision for any intermediate level of
 file access. In e-TeX, we provide facilities for 
 <code>\input</code>ting one or more named modules from a
 suitably structured library file. The syntax used is: 
<pre>
 \load &lt;module&gt;[, &lt;module&gt;...] from &lt;file&gt;
</pre>
 whilst the library file itself should be structured as:
<pre>
 %% e-TeXlib Vx.y
 \module {&lt;name&gt;}
 . . .
 \endmodule

\module {&lt;name&gt;}
 . . .
 \endmodule
 
 etc. 
</pre>
 The %% header is required, and the actual values in
	<code>Vx.y</code> must correspond to the current version/revision
 of e-TeX; for the current release, the header must therefore
 be:
<pre>
 %% e-TeXlib V2.0
</pre>
 If a library file is changed during the lifetime of the system, it
 is recommended (but not required) that this amendment be
 recorded in a cycle number appended to the header;
 a cycle number is of the form <code>;</code>digit[s],
 and thus a valid header for the current release of e-TeX might be
 any of:
<pre>
 %% e-TeXlib V2.0
 %% e-TeXlib V2.0;1
 %% e-TeXlib V2.0;247
</pre>
 etc. The necessity for a perfect match between the library header
 and the current version/revision of e-TeX may be relaxed in a future
 release if it transpires that no changes in the structure of user
 libraries are required for compatibility with future versions of e-TeX.
 
</dd>

<dt>Modules in the standard library (<code>etexdefs.lib</code>)</dt>
<dd>
e-TeX is distributed with a standard library which provides mnemonic
names for the various values which can be returned by the new primitives.
The library contains four modules: 
<code>grouptypes</code>,
<code>nodetypes</code>,
<code>interactionmodes</code> and
<code>iftypes</code>. The standard format source, <code>etex.src</code>,
loads <code>interactionmodes</code> by default; the others can be loaded
using the appropriate one of the following:
<pre>
	\load grouptypes from etexdefs.lib
	\load nodetypes from etexdefs.lib
	\load iftypes from etexdefs.lib
</pre>
Once the relevant module has been loaded, the numeric values
associated with each of the possible types/modes can be retrieved
using one of the following commands with one of the parameters shewn:
<pre>
	\grouptypes
			{simple}
			{hbox}
			{adjustedhbox}
			{vbox}
			{vtop}
			{align}
			{noalign}
			{output}
			{math}
			{disc}
			{insert}
			{vcenter}
			{mathchoice}
			{semisimple}
			{mathshift}
			{mathleft}

\nodetypes
			{char}
			{hlist}
			{vlist}
			{rule}
			{ins}
			{mark}
			{adjust}
			{ligature}
			{disc}
			{whatsit}
			{math}
			{glue}
			{kern}
			{penalty}
			{unset}
			{maths}

\conditionaltypes
			{charif}
			{catif}
			{numif}
			{dimif}
			{oddif}
			{vmodeif}
			{hmodeif}
			{mmodeif}
			{innerif}
			{voidif}
			{hboxif}
			{vboxif}
			{xif}
			{eofif}
			{trueif}
			{falseif}
			{caseif}
			{definedif}
			{csnameif}
			{fontcharif}

\interactionmodes
			{batch}
			{nonstop}
			{scroll}
			{errorstop}
</pre>
</dd>

<dt>Multiple language typesetting</dt>
<dd>When TeX gained <code>\language</code> and
 <code>\setlanguage</code> primitives with the advent of TeX 3.0, no
 change was made to the Plain TeX source code to really exploit these
 features with the single exception of the <code>\newlanguage</code>
 command. In "<code>etex.src</code>", we defer the loading of
 patterns and hyphenation exceptions until a
 rudimentary language handling environment has been defined. We now
 assume that the user (or rather the format-creator) will,
	if required, modify the file
 called "<code>language.def</code>" by adding the
 various languages to be supported by the format. Each entry apart from
 the last in "<code>language.def</code>" is of the form: 
<pre>
 \addlanguage {&lt;language&gt;}
 {&lt;patterns file&gt;}
 {&lt;exceptions file&gt;}
 {&lt;left hyphen min&gt;}
 {&lt;right hyphen min&gt;} %%% shewn wrapped for clarity
</pre>
 The first line must be:
<pre>
 \addlanguage {USenglish}{hyphen.tex}{}{2}{3}
</pre>
 whilst the last must be
<pre>
 \uselanguage {USenglish}
</pre>
 to ensure that legacy documents not explicitly specifying a language
	process in a manner identical to TeX (that is, using American English
	patterns, exceptions and left- and right-hyphen minima).
 In the absence of a suitable <code>language.def</code>
 file, the default fallback mode (USenglish, with the canonical patterns,
 exceptions and left- and right-hyphen minima for TeX) will be used.
 Within the user document, <code>\uselanguage {&lt;some
 language&gt;}</code> should be used to switch languages, which
 will have the effect of loading appropriate patterns, exceptions, and
 left- and right hyphen minima. To allow the use of more powerful
 language-handling environments (e.g.&nbsp;<a
 href="http://homepage.cistron.nl/~jlbraams/babel.html">Babel</a>),
 the <code>\uselanguage</code> command finishes by testing whether the
 putative control sequence <code>\uselanguage@hook</code> is defined; if
 it is, then it is expanded, passing as parameter the name of the
 language to be used. It should be noted that <code>\uselanguage</code>
	is automatically invoked during the expansion of 
	<code>\addlanguage</code> prior to the reading of patterns; 
	a further hook, <code>\addlanguage@hook</code>, is invoked in an
	identical manner after the reading of patterns and exceptions
	so as to allow (for example) category-codes to be changed for the
	duration of the pattern- and exception-loading r�gime. This code is 
	still classed as experimental, and if it transpires that a superior 
	mechanism would improve the interface to 
 <a href="http://homepage.cistron.nl/~jlbraams/babel.html">Babel</a>
 or <a href="http://www.tex.ac.uk/CTAN/latex/">LaTeX</a>, it may be
 enhanced in the future. 
 
</dd>
</dl>

The e-TeX format source "etex.src" is a product of 
<a href="/e-TeX/NTS-Group.Html">the NTS group</a>. 
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