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B.16 Extra Features
This section describes HEVEA functionalities that extends on plain LATEX, as defined in [LATEX]. Most of the features described here are performed by default.

B.16.1 Accents in maths
Loading the mathaccents.hva style files enables default typesetting of the math accents commands (\hat, \tilde,...), see Section B.7.4.

B.16.2 TeX macros
Normally, HEVEA does not recognize constructs that are specific to TeX. However, some of the internal commands of HEVEA are homonymous to TeX macros, in order to enhance compatibility. Note that full compatibility with TeX is not guaranteed.

B.16.2.1 la TeX macros definitions
The \def construct for defining commands is supported. It is important to notice that HEVEA semantics for \def follows TeX semantics. That is, defining a command that already exists with \def succeeds. This is an important change with respect to previous versions of HEVEA, where \def had the same semantics as \newcommand.

Delimiting characters in command definition are supported. Consider the following example from the TeX Book:
\def\Look{\textsc{Look}}
\def\x{\textsc{x}}
\def\cs AB#1#2C$#3\$ {#3{ab#1}#1 c\x #2}
\cs AB {\Look}{}C${And \$}{look}\$ 5.
It yields: And $lookabLookLook cx5.

Please note that delimiting characters are supported as far as I could, problems are likely with delimiting characters which include spaces or command names, in particular the command name \{. One can include \{ in a command argument by using the grouping characters {... }:
\def\frenchquote(#1){~\emph{#1}~ (in French)}
He said \frenchquote(Alors cette accolade ouvrante {``\{''}~?).
Yields:
He said  Alors cette accolade ouvrante ``{'' ?  (in French).

Another source of incompatibilty with TeX is that substitution of macros parameters is not performed at the same moment by HEVEA and TeX. However, things should go smoothly at the first level of macro expansion, that is when the delimiters appear in source code at the same level as the macro that is to parse them. For instance, the following source will give different results in LATEX and in HEVEA:
\def\cs#1A{``#1''}
\def\othercs#1{\cs#1A}
\othercs{coucouA}
LATEX output is ``coucou''A, while HEVEA output is ``coucouA''. Here is HEVEA output: ``coucouA'' Please note that in most situations this discrepancy will make HEVEA crash.

B.16.2.2 The \let construct
HEVEA also processes a limited version of \let:
\let macro-name1 = macro-name2
The effect is to bind macro-name1 to whatever macro-name2 is bound to at the time \let is processed. This construct may prove very useful in situations where one whishes to slightly modify basic commands. See sections 9.3 and B.2 for examples of using \let in such a situation.

B.16.2.3 The \global construct
It is possible to escape scope and to make global definitions and bindings by using the TeX construct \global. The \global construct is significant before \def and \let constructs.

Also note that \gdef is equivalent to \global\def.

B.16.2.4 TeX Conditional Macros
The \newif\ifname, where name is made of letters only, creates three macros: \ifname, \nametrue and \namefalse. The latter two set the name condition to true and false, respectively. The \ifname command tests the condition name:
\ifname
text1

\else
text2
\fi
Text text1 is processed when name is true, otherwise text2 is processed. If text2 is empty, then the \else keyword can be omitted.

Note that HEVEA also implements LATEX ifthen package and that TeX simple conditional macros are fully compatible with LATEX boolean registers. More precisely, we have the following correspondences:
TeX LATEX
\newifname    \newboolean{name}
\nametrue    \setboolean{name}{true}
\namefalse    \setboolean{name}{false}
\ifname text1\else text2\fi    \ifthenelse{\boolean{name}}{text1}{text2}

B.16.2.5 Other TeX Macros
HEVEA implements the macros \unskip and \endinput. It also supports the \csname... \endcsname construct.

B.16.3 Command Definition inside Command Definition
If one strictly follows the LATEX manual, only commands with no arguments can be defined inside other commands. Parameters (i.e., #n) occurring inside command bodies refer to the outer definition, even when they appear in nested command definitions. That is, the following source:
\newcommand{\outercom}[1]{\newcommand{\insidecom}{#1}\insidecom}
\outercom{outer}
yields this output:
outer

Nevertheless, nested commands with arguments are allowed. Standard parameters #n still refer to the outer definition, while nested parameters ##n refer to the inner definition. That is, the source:
\newcommand{\outercom}[1]{\newcommand{\insidecom}[1]{##1}\insidecom{inner}}
\outercom{outer}
yields this output:
inner

B.16.4 Date and time
Date and time support is not enabled by default, for portability and simplicity reasons.

However, HEVEA source distribution includes a simple (sh) shell script xxdate.exe that activates date and time support. The hevea command, should be invoked as :
# hevea -exec xxdate.exe ...
This will execute the script xxdate.exe, whose output is then read by HEVEA. As a consequence, standard TeX counters \year, \month, \day and \time are defined and LATEX command \today works properly. Additionnally the following counters and commands are defined :
    
Counter weekday    day of week, 0...6 (e.g. 2)
Counter Hour    hour, 00...11 (e.g. 11)
Counter hour    hour, 00...23 (e.g. 11)
Counter minute    minute, 00...59 (e.g. 35)
Counter second    second, 00...611 (e.g. 57)
Command \ampm    AM or PM (e.g. AM)
Command \timezone    Time zone (e.g. CEST)
Command \heveadate    Output of the ``date'' Unix command, (e.g. mar mai 21 11:35:57 CEST 2002)

Note that I choosed to add an extra option (and not an extra ``\@exec'' primitive) for security reasons. You certainly do not want to enable HEVEA to execute silently an arbitrary program without being conscious of that fact. Moreover, the hevea program does not execute xxdate.exe by default since it is difficult to write such a script in a portable manner.

Windows users should enjoy the same features with the version of xxdate.exe included in the Win32 distribution.

B.16.5 Fancy sectioning commands
Loading the fancysection.hva file will radically change the style of sectionnal units headers: they appear over a green backgroud, the backgrould color saturation decreases as the sectioning commands themselves do (this is the style of this manual). Additionnaly, the document background color is white.

The fancysection.hva file is intended to be loaded after the document base style. Thus, to use fancy section style in doc.tex whose base style is article you should issue the command:
# hevea article.hva fancysection.hva doc.tex
You can also make a doc.hva file that contains the two lines:
\input{article.hva}
\input{fancysection.hva}
And then launch hevea as:
# hevea doc.hva doc.tex
Sectioning command background colors can be changed by redefining the corresponding colors (part, chapter, section,...). For instance, you get various mixes of red and orange by:
\input{article.hva}
\input{fancysection.hva}
\definecolor{part}{named}{BrickRed}
\definecolor{section}{named}{RedOrange}
\definecolor{subsection}{named}{BurntOrange}
(See section B.14.2 for details on the named color model that is used above.)

Another choice is issuing the command \colorsection{hue}, where hue is a hue value to be interpreted in the HSV model. For instance,
\input{article.hva}
\input{fancysection.hva}
\colorsections{20}
will yield sectionnal headers on a red-orange background.

B.16.6 HEVEA as a Back-End for VideoC
HEVEA is one of the back-ends of the VideoC system for producing educational CDROM to teach programming languages. VideoC author is Christian Queinnec and the documentation is available at:
http://www-spi.lip6.fr/~queinnec/VideoC/VideoC.html.

VideoC translates LATEX source into a variety of formats, including HTML. VideoC source may contain some special constructs for typesetting source code or to annotate text in sophisticated ways. HEVEA internal engine implements some of the core constructs needed by VideoC. The rest of VideoC constructs are implemented by the .hva files from VideoC distribution.


1
According to date man page.

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