Provided by: wml_2.32.0~ds1-1_all 
NAME
WML Tutorial - Understanding WML step-by-step
DESCRIPTION
This tutorial gives you a step-by-step introduction to the features of WML, separated into tiny lessons.
Each lesson shows one particular aspect or feature of WML. The order of lessons go from easy and trivial
to hard and complex.
IMPLICIT MARKUP PROCESSING
LESSON: Plain Data Throughput
In this lesson we first learn that WML is 95% of the time transparent to its input, i.e. we can pass
through any data without corruption.
Input:
1| foo
2| <bar>
3| quux
Output:
1| foo
2| <bar>
3| quux
This is because per default there are neither definitions for symbols "foo" or "quux" nor a defined HTML
tag named "<bar>". And because there are no unnecessary whitespaces in this example, the input cannot be
stripped in any case.
LESSON: Protected Markup Code
Sometimes situations can occur where some of your markup code or page contents conflicts with WML due to
overlapping tagnames, etc. Here WML interprets some stuff you actually don't want to be interpreted.
Input:
1| foo: foo.c
2| $(CC) -o foo foo.c
Output:
1| foo: foo.c
2| -o foo foo.c
Here the `"$(CC)"' was expanded to an empty string because IPP uses the same syntax for variable
interpolation like make. To avoid this just surround the critical part with the WML-internal "<protect>"
container tag.
Input:
1| foo: foo.c
2| <protect>$(CC)</protect> -o foo foo.c
Output:
1| foo: foo.c
2| $(CC) -o foo foo.c
LESSON: Stripped-Down Markup Code
Now let's try an example which has unnecessary whitespaces. Be careful, `unnecessary' here means they can
be stripped as long as the resulting Webpage displays the same in a Webbrowser as the original.
Input:
1| <body>
2|
3| <img src = "file.gif" alt=" test " >
4| <pre>
5|
6| Preformatted Text
7| </pre>
8| Not Preformatted Text
9| </body>
Output:
1| <body>
2| <img src="file.gif" alt=" test ">
4| <pre>
5|
6| Preformatted Text
7| </pre>
8| Not Preformatted Text
9| </body>
Here we see that line 2 is completely removed because empty lines have no effect in HTML. The whitespaces
between the attribute "src" and its value are removed, too. And all double whitespaces are replaced by a
single whitespace character. But not inside preformatted areas.
LESSON: Fixed And Adjusted Markup Code
Now assume that we have an image.gif file containing a GIF image with a size of 500x400 pixels and the
following input page:
1| <body>
2| <center>
3| <font color=336699>Headline:</font><br>
4| <img src="image.gif">
5| </center>
6| </body>
Although this is valid HTML code, WML can enhance it to make it more portable, speed up it rendering in
the Webbrowser and make Lynx users more happy. So WML recognizes the "<img>" tag and automatically adds
missing information and replaces obsolete tags with up-to-date variants:
1| <body>
2| <div align=center>
3| <font color="#336699">Headline:</font><br>
4| <img src="image.gif" alt="" width="500" height="400">
5| </div>
6| </body>
As you can see, WML first replaced the proprietary "<center>" tag with the HTML 3.2 pedant "<div
align=center>", second it fixed the "color" attribute of "<font>". And third it added missing "alt" and
"width"/"height" attributes.
STRUCTURING THE MARKUP CODE
LESSON: Using Include Files
One of the most useful features of WML is the ability to move commonly used stuff into include files
which can be selectively read in at later steps.
Assume we have an include file bar.wml...
1| bar
2| The value of bar is: $(bar:-unknown)
...and the following input file:
1| foo
3| #include 'bar.wml' bar="FooBar"
2| #include 'bar.wml'
5| quux
Then the output is:
1| foo
2| bar
3| The value of bar is: Foobar
4| bar
5| The value of bar is: unknown
6| quux
As you can see, the "#include" directive is replaced by the contents of the corresponding file. And this
included contents can contain variables which are interpolated when they are defined, inclusive default
values.
There is also a way to create simple constructs similar to an if-then-else just by using variable
interpolation:
1| The value of bar is $(bar:+set)$(bar:*unset).
Here the `"$(bar:+set)$(bar:*unset)"' construct emulates the following semantics:
if (isdefined(bar))
expandto("set")
if (not isdefined(bar))
expandto("unset")
LESSON: Concatenating Lines
Although HTML usually does not care about whitespaces and newlines, sometimes it is very frustrating to
create preformatted areas or write own tags (see later) without the ability to spread the code over more
than one line while it should be actually one single line. For this a lot of languages use a line
concatenation/continuation character `"\"', as does WML.
Input:
1| foo\
2| bar \
3| quux
Output:
1| foobar quux
The line concatenation strips whitespaces from the begin of concatenated lines but preserves whitespaces
at the end of them, i.e. you can use leading whitespaces for structuring your input nicely but still use
appended whitespaces for real ones.
LESSON: Diverting To Locations
One of the most powerful features of WML is the ability to divert data at any point to locations defined
at any other point.
Input:
1| {#BAR#:this is:##}
2| foo
3| {#BAR#}
4| quux
5| {#BAR#: bar:##}
6| foobar
7| {#BAR#}
Output:
1| foo
2| this is bar
3| quux
4| foobar
5| this is bar
Here in line 3 the location "BAR" is already dumped, but filled at lines 1 and 5. And as you can see a
location can be dumped at any point and even more than once. And you can accumulate the contents for a
location by subsequent fills (line 1 and 5). This works because in WML first all locations are filled in
a first pass and then dumped in a second pass.
With the use of the high-level tags from wml::std::tags we also could write the example above in a little
bit more human readable way:
1| #use wml::std::tags
2| <divert BAR>this is</divert>
3| foo
4| <dump BAR>
5| quux
6| <divert BAR> bar</divert>
7| foobar
8| <dump BAR>
LESSON: Defining Output Slices
Often one needs more than one output file. Usually although 90% of the contents is the same, one needs a
way to select the remaining 10%. WML's approach here is to write these 10% directly in the input file but
separate the variants by defining slices which later can be used to create the different output files.
1| <html>
2| <head>
3| <title>[EN:Titleline:][DE:Titelzeile:]</title>
4| </head>
5| <body>
6| <h1>[EN:Headerline:][DE:Ueberschrift:]</h1>
7| </body>
8| </html>
Now assume the above page is in file index.wml, then the command
$ wml -o UNDEF+EN:index.html.en \
-o UNDEF+DE:index.html.de index.wml
generates the output file "index.html.en" containing the union of all undefined areas and the slices
`"EN"'...
1| <html>
2| <head>
3| <title>Titleline</title>
4| </head>
5| <body>
6| <h1>Headerline</h1>
7| </body>
8| </html>
...and the output file "index.html.de" containing the union of all undefined areas and the slices `"DE"':
1| <html>
2| <head>
3| <title>Titelzeile</title>
4| </head>
5| <body>
6| <h1>Ueberschrift</h1>
7| </body>
8| </html>
FORMATTING
LESSON: Area Substitution
WML provides an area substitution feature which works by specifying the begin and end of the area and
inserting some Perl substitution and translation commands.
Input:
1| foo
2| {: [[s/foo/bar/g]] [[s/quux/foobar/g]] [[tr/[a-z]/[A-Z]/]]
3| this is foo and quux.
4| :}
5| quux
Output:
1| foo
2| THIS IS BAR AND FOOBAR.
3| quux
Because this seems useless, we go further and show an example of the "<isolatin>" and "<url>" container
tags from wml::fmt::isolatin and wml::fmt::url which are programmed this way.
Input:
1| #use wml::fmt::isolatin
2| #use wml::fmt::url
3| <isolatin><url>
4| Some umlauts `XXXXXX' and
5| a hyperlink http://foo.bar.com/
6| </url></isolatin>
Output:
1| Some umlauts `öäüÖÄß' and
2| a hyperlink <a href="http://foo.bar.com/">http://foo.bar.com/</a>
LESSON: Text Formatting
HTML sucks when it comes to write more than one paragraph of text. So WML provides nice ways to format
an area of input via other (externally available) markup language processors. Here is an example which
used two embedded areas, the first one is written in Plain Old Document (POD) format, second one is
written in Simple Document Format (SDF).
Input:
1| #use wml::fmt::pod
2| #use wml::fmt::sdf
3| <html>
4| <pod notypo>
5| =head1 Headline1
6|
7| Foo
8|
9| =head2 Headline1.1
10|
11| Bar
12| </pod>
13|
14| <sdf notypo>
15| H1: Headline1
16|
17| Foo
18|
19| H2: Headline 1.1
20|
21| Bar
22| * Baz
23| - Foobar
24| - Quux
25| * Foo
26| </sdf>
27| </html>
Output:
1| <html>
2| <P>
3| <H1><A NAME="Headline1">Headline1
4| </A></H1>
5| Foo
6| <P>
7| <H2><A NAME="Headline1_1">Headline1.1
8| </A></H2>
9| Bar
10| <P>
11| <H1><A NAME="Headline1">1. Headline1</A></H1>
12| <P>Foo</P>
13| <H2><A NAME="Headline 1.1">1.1. Headline 1.1</A></H2>
14| <P>Bar</P>
15| <UL>
16| <LI>Baz<UL>
17| <LI>Foobar
18| <LI>Quux</UL>
19| <LI>Foo</UL>
20| </html>
LESSON: Table Formatting
Another point where the HTML markup code is unproductive and ugly is when it comes to write some
"<table>" structures. Here WML provides two new container tags which make your live easier:
<grid>
The goal of this container tag is to provide a way to specify tables the same way you have it in your
mind, i.e. as a 2-dimensional grid. So, a grid is created by specifying a grid-layout and then fill
its cells. Additionally the "<grid>" container tag provides a nice feature for specifying the cell
alignments.
Input:
1| #use wml::std::grid
2| <grid layout=2x3 align=lr valign=tbb border=1>
3| <cell>Header 1</cell> <cell>Header 2</cell>
4| <cell>Cell-A</cell> <cell>Cell-B</cell>
5| <cell>Cell-C</cell> <cell>Cell-D</cell>
6| </grid>
Output:
1| <table border="1" cellspacing="0" cellpadding="0">
2| <tr>
3| <td align=left valign=top>Header 1</td>
4| <td align=right valign=top>Header 2</td>
5| </tr>
6| <tr>
7| <td align=left valign=bottom>Cell-A</td>
8| <td align=right valign=bottom>Cell-B</td>
9| </tr>
10| <tr>
11| <td align=left valign=bottom>Cell-C</td>
12| <td align=right valign=bottom>Cell-D</td>
13| </tr>
14| </table>
<xtable>
This is the extended "<table>" container tag which syntax is provided by the external freetable
program. Its goal is to provide a compact syntax for specifying a table. Again the same example:
Input:
1| #use wml::fmt::xtable
2| <xtable border=1>
3| (*, 1) align=left
4| (*, 2) align=right
5| (1, *) valign=top
6| (2|3, *) valign=bottom
7| (1,1)
8| Header 1
9| (1,2)
10| Header 2
11| (2,1)
12| Cell-A
13| (2,2)
14| Cell-B
15| (3,1)
16| Cell-C
17| (3,2)
18| Cell-D
19| </xtable>
Output:
1| <table border="1">
2| <tr valign=top>
3| <td align=left>Header 1</td>
4| <td align=right>Header 2</td>
5| </tr>
6| <tr>
7| <td align=left valign=bottom>Cell-A</td>
8| <td align=right valign=bottom>Cell-B</td>
9| </tr>
10| <tr>
11| <td align=left valign=bottom>Cell-C</td>
12| <td align=right valign=bottom>Cell-D</td>
13| </tr>
14| </table>
DEFINITION OF OWN HTML TAGS
LESSON: Simple Tags And Container Tags
Now it is time to enhance our markup language by defining new custom HTML tags. There are two types of
HTML tags:
Simple Tags
As an example let us define a "<me>" tag which expands to my name abbreviation.
Input:
1| <define-tag me whitespace=delete>
2| rse@engelschall.com
3| </define-tag>
4|
5| This is <me>.
Output:
1| This is rse@engelschall.com.
Container Tags
As an example let us define a "<red>" tag which changes its body text color to red.
Input:
1| <define-tag red endtag=required whitespace=delete>
2| <font color="#cc3333">%body</font>
3| </define-tag>
4|
5| This is <red>very important</red>.
Output:
1| This is <font color="#cc3333">very important</font>.
LESSON: Tags With Attributes
Because tags without attributes are not very flexible there is also a way to define tags which can use
these.
Input:
1| <define-tag me whitespace=delete>
2| <if "%0" "" "rse@engelschall.com">
3| <ifeq "%0" "engelschall" "rse@engelschall.com">
4| <ifeq "%0" "netsw" "rse@netsw.org">
5| <ifeq "%0" "apache" "rse@apache.org">
6| <ifeq "%0" "freebsd" "rse@freebsd.org">
7| <ifeq "%0" "sdm" "rse@sdm.de">
8| </define-tag>
9|
10| This is <me> and <me apache>.
Output:
1| This is rse@engelschall.com and rse@apache.org.
There is also a variant to use attributes of type "name=value":
Input:
2| <define-tag me whitespace=delete>
3| <preserve at>
4| <set-var %attributes>
5| <if "<get-var at>" "" "rse@engelschall.com">
6| <ifeq "<get-var at>" "engelschall" "rse@engelschall.com">
7| <ifeq "<get-var at>" "netsw" "rse@netsw.org">
8| <ifeq "<get-var at>" "apache" "rse@apache.org">
9| <ifeq "<get-var at>" "freebsd" "rse@freebsd.org">
10| <ifeq "<get-var at>" "sdm" "rse@sdm.de">
11| <restore at>
12| </define-tag>
13|
14| This is <me> and <me at=apache>.
Output:
1| This is rse@engelschall.com and rse@apache.org.
LESSON: Overwriting Existing HTML Tags
WML also provides a way to overwrite existing HTML tags, i.e. you can define a custom tag with the same
name as an already known HTML tag and use the original HTML tag inside it.
Input:
1| <define-tag br whitespace=delete>
2| <br*><br*>
4| </define-tag>
5|
6| Some Text<br>
7| Some more Text
Output:
1| Some Text<br><br>
2| Some more Text
LESSON: Programming Tags In Perl
One of the essential features in WML is that you can embed Perl code at any point, just marked with
`"<:"' and `":>"' delimiters. This can be combined with the tag definitions by programming tags in Perl.
Input:
1| #use wml::std::tags
2| <define-tag me whitespace=delete>
3| <preserve at>
4| <set-var %attributes>
5| <:{
6| my $at = qq/<get-var at>/;
7| my $addr;
8| $addr = "rse\@engelschall.com" if $at eq '';
9| $addr = "rse\@engelschall.com" if $at eq 'engelschall';
10| $addr = "rse\@netsw.org" if $at eq 'netsw';
11| $addr = "rse\@apache.org" if $at eq 'apache';
12| $addr = "rse\@freebsd.org" if $at eq 'freebsd';
13| $addr = "rse\@sdm.de" if $at eq 'sdm';
14| print $addr;
15| }:>
16| <restore at>
17| </define-tag>
18|
19| This is <me> and <me at=apache>.
Output:
1| This is rse@engelschall.com and rse@apache.org.
ADVANCED FEATURES
LESSON: Using Templates
We've already seen how to divert data to a location. Because WML automatically closes still opened
diversions at EndOfFile, we can use this feature to create templates. Assume we have the following
template defined in the file template.wml.
1| # the template itself
2| <html>
3| <head>
4| <title>{#SUBJECT_LOC#}</title>
5| </head>
6| <body>
7| <h1>{#SUBJECT_LOC#}</h1>
8| <blockquote>
9| {#BODY#}
10| </blockquote>
11| </body>
12| </html>
13|
14| # way to insert the subject
15| <define-tag subject>
16| {#SUBJECT_LOC#:%0:##}
17| </define-tag>
18|
19| # per default we are in body
20| {#BODY#:
Input:
1| #include 'template.wml'
2|
3| <subject "Foo, Bar and Quux">
4|
5| This is about Foo, Bar and Quux...
Output:
1| <html>
2| <head>
3| <title>Foo, Bar and Quux</title>
4| </head>
5| <body>
6| <h1>Foo, Bar and Quux</h1>
7| <blockquote>
8| This is about Foo, Bar and Quux...
9| </blockquote>
10| </body>
11| </html>
You can even nest more than one template because the diversion mechanism in WML accepts location dumps
and location fills at any point, even within other location fills.
LESSON: Creating Multi-Lingual Pages
The core languages of WML don't provide a dedicated facility to create multi-lingual pages, i.e. one or
more output pages created out of a single input source, each one containing the same page information but
in different human languages. But WML provides variants through ``slicing'' (Pass 9) and human languages
are just a special case of general variants. So wml::std::lang exists which provides specialized multi-
lingual support tags which are mapped to slices which then can be used to create the various output
files.
Let take an example:
1| #!wml -o (ALL-LANG_*)+LANG_EN:index.en.html \
2| -o (ALL-LANG_*)+LANG_DE:index.de.html
3|
4| #use wml::std::page
5| #use wml::std::lang
6|
7| <lang:new id=en short>
8| <lang:new id=de short>
9|
10| <page>
11|
12| <h1><en: Welcome><de: Willkommen>!</h1>
13|
14| <a href="<lang:star: index2.*.html>">Index 2</a>
15|
16| <lang:area>
17| (en)This is a test page
18| (de)Dies ist eine Testseite
19| </lang:area>
After processing passes 1 to 8 ("wml -p1-8") the following is internally generated by WML:
1| <html>
2| <head>
3| </head>
4| <body bgcolor="#ffffff" text="#000000" link="#333399" alink="#9999ff" vlink="#000066">
5| <h1>[LANG_EN:Welcome:][LANG_DE:Willkommen:]!</h1>
6| <a href="[LANG_EN:index2.en.html:][LANG_DE:index2.de.html:]">Index 2</a>
7| [LANG_EN:This is a test page
8| :][LANG_DE:Dies ist eine Testseite:]
9| </body>
10| </html>
And then after processing pass 9 with the initial WML magic cookie line ("#!wml -o...") the following two
files are generated:
index.en.html:
1| <html>
2| <head>
3| </head>
4| <body bgcolor="#ffffff" text="#000000" link="#333399" alink="#9999ff" vlink="#000066">
5| <h1>Welcome!</h1>
6| <a href="index2.en.html">Index 2</a>
7| This is a test page
8|
9| </body>
10| </html>
index.de.html:
1| <html>
2| <head>
3| </head>
4| <body bgcolor="#ffffff" text="#000000" link="#333399" alink="#9999ff" vlink="#000066">
5| <h1>Willkommen!</h1>
6| <a href="index2.de.html">Index 2</a>
7| Dies ist eine Testseite
8| </body>
9| </html>
And these two pages then can be served by a content negotiation feature of the webserver or by explicit
references.
MORE INFORMATION
Now you've seen the various core languages of WML in action. For the gory details of what each language
provides either read the all-in-one WML Introduction in wml_intro(7) or step through the particular
manpages of the core languages. Start here with the frontend wml(1).
Additionally can can step through the set of available standard include files WML ships with. Start with
the top-level include file wml::all(3).
SEE ALSO
wml_intro(7)
wml_p1_ipp(3), mp4h(1), eperl(1), m4(1), wml_p5_divert(3), wml_p6_asubst(3), wml_p7_htmlfix(3),
wml_p8_htmlstrip(3), slice(1).
wml::all(3)