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"http://www.w3.org/TR/REC-html40/loose.dtd"> Customizing HEVEA
 9 Customizing HEVEA
HEVEA can be controlled by writing LATEX code. In this section, we examine how users can change HEVEA default behavior or add functionalities. In all this section we assume that a document mydoc.tex is processed, using a private command file macros.hva. That is, HEVEA is invoked as:
# hevea macros.hva mydoc.tex

The general idea is as follows: one redefines LATEX constructs in macros.hva, using internal commands. This requires a good working knowledge of both LATEX and HTML. Usually, one can avoid internal commands, but then, all command redefinitions interact, sometimes in very nasty ways.

 9.1 Simple changes
Users can easily change the rendering of some constructs. For instance, assume that all quotations in a text should be emphasized. Then, it suffices to put the following redeclaration in macros.hva:
\renewenvironment{quote}
{\@open{BLOCKQUOTE}{}\@style{EM}}
{\@close{BLOCKQUOTE}}

The same effect can be achieved without using any of the internal commands:
\let\oldquote\quote
\let\oldendquote\endquote
\renewenvironment{quote}{\oldquote\em}{\oldendquote}

In some sense, this second solution is easier, when one already knows how to customize LATEX. However, this is less safe, since the definition of \em can be changed elsewhere.

 9.2 Changing defaults for type-styles

HEVEA default rendering of type style changes is described in section B.15.1. For instance, the following example shows the default rendering for the font shapes:
\itshape italic shape \slshape slanted shape
\scshape small caps shape \upshape upright shape

By default, \itshape is italics, \slshape is maroon italics, \scshape is navy blue color and \upshape is no style at all. All shapes are mutually exclusive, this means that each shape declaration cancels the effect of other active shape declarations. For instance, in the example, small caps shapes is navy blue and not navy blue italics.

italic shape slanted shape small caps shape upright shape
If one wishes to change the rendering of some of the shapes (say small caps), then one should redefine the old-style \sc declaration. For instance, to render small caps as bold fonts, one should redefine \sc by \renewcommand{\sc}{\@style{B}} in macros.hva.

And now, the shape example above gets rendered as follows:

italic shape slanted shape small caps shape upright shape
Redefining the old-style \sc is compatible with the cancelation mechanism, redefining \scshape is not. Thus, redefining directly LATEX 2e \scshape with \renewcommand{\scshape}{\@style{B}} would yield:

italic shape slanted shape small caps shape upright shape
Hence, redefining old-style declarations using internal commands should yield satisfactory output. However, since cancelation is done at the HTML level, a declaration belonging to one component may sometimes cancel the effect of another that belongs to another component. Anyway, you might have not noticed it if I had not told you.

 9.3 Changing the interface of a command
Assume for instance that the base style of mydoc.tex is jsc (the Journal of Symbolic Computation style for articles). For running HEVEA, the jsc style can be replaced by article style, but for a few commands whose calling interface is changed. In particular, the \title command takes an extra optional argument (which HEVEA should ignore anyway). However, HEVEA can process the document as it stands. One solution to insert the following lines into macros.hva:
\input{article.hva}% Force document class article''
\let\oldtitle=\title
\renewcommand{\title}[2][]{\oldtitle{#2}}

The effect is to replace \title by a new command which calls HEVEA \title with the appropriate argument.
 9.4 Checking the optional argument within a command
HEVEA fully implements LATEX 2e \newcommand. That is, users can define commands with an optional argument. Such a feature permits to write a \epsfbox command that has the same interface as the LATEX command and echoes itself as it is invoked to the image file. To do this, the HEVEA \epsfbox command has to check whether it is invoked with an optional argument or not. This can be achieved as follows :
\newcommand{\epsfbox}[2][!*!]{%
\ifthenelse{\equal{#1}{!*!}}
{\begin{toimage}\epsfbox{#2}\end{toimage}}%No optional argument
{\begin{toimage}\epsfbox[#1]{#2}\end{toimage}}}%With optional argument
\imageflush}

 9.5 Changing the Format of Images
Semi-automatic generation of included images is described in section 6.

Links to included images are generated by the \imageflush command, which calls the \imgsrc command :
\newcommand{\imageflush}[1][]
{\@imageflush\stepcounter{image}\imgsrc[#1]{\jobname\theimage\heveaimageext}}

That is, you may supply a HTML-style attribute to the included image, as an optional argument to the \imageflush command.

By default, images are GIF images, stored in .gif'' files. HEVEA provides direct support for the alternative PNG image file format. It suffices to invoke hevea as:
# hevea png.hva mydoc.tex

Then imagen must be run as:
# imagen -png mydoc

Beware that transparent colors are not shown correctly by my browser for PNG images, while they work as advertised for GIF images. This does not harm as long as the final HTML document has a white background color (see Section B.2).