Documentation: Tutorial

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Tutorial - Understanding WML step-by-step


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| _lbrace_#BAR#:this is:##_rbrace_
 2| foo
 3| _lbrace_#BAR#_rbrace_
 4| quux
 5| _lbrace_#BAR#: bar:##_rbrace_
 6| foobar
 7| _lbrace_#BAR#_rbrace_

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>_lbrack_EN:Titleline:_rbrack__lbrack_DE:Titelzeile:_rbrack_</title>
 4| </head>
 5| <body>
 6| <h1>_lbrack_EN:Headerline:_rbrack__lbrack_DE:Ueberschrift:_rbrack_</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| _lbrace_: _lbrack__lbrack_s/foo/bar/g_rbrack__rbrack_ _lbrack__lbrack_s/quux/foobar/g_rbrack__rbrack_ _lbrack__lbrack_tr/_lbrack_a-z_rbrack_/_lbrack_A-Z_rbrack_/_rbrack__rbrack_
 3| this is foo and quux.
 4| :_rbrace_
 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 `' and
 5| a hyperlink http://foo.bar.com/
 6| </url></isolatin>

Output:

 1| Some umlauts `&ouml;&auml;&uuml;&Ouml;&Auml;&szlig;' 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 wml_aux_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| <:_lbrace_
  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| _rbrace_:>
 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>_lbrace_#SUBJECT_LOC#_rbrace_</title>
  5| </head>
  6| <body>
  7| <h1>_lbrace_#SUBJECT_LOC#_rbrace_</h1>
  8| <blockquote>
  9| _lbrace_#BODY#_rbrace_
 10| </blockquote>
 11| </body>
 12| </html>
 13|
 14| #   way to insert the subject
 15| <define-tag subject>
 16| _lbrace_#SUBJECT_LOC#:%0:##_rbrace_
 17| </define-tag>
 18|
 19| #   per default we are in body
 20| _lbrace_#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>_lbrack_LANG_EN:Welcome:_rbrack__lbrack_LANG_DE:Willkommen:_rbrack_!</h1>
  6| <a href="_lbrack_LANG_EN:index2.en.html:_rbrack__lbrack_LANG_DE:index2.de.html:_rbrack_">Index 2</a>
  7| _lbrack_LANG_EN:This is a test page
  8| :_rbrack__lbrack_LANG_DE:Dies ist eine Testseite:_rbrack_
  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).


SEEALSO

wml_intro(7)

wml_p1_ipp(1), wml_p2_mp4h(1), wml_p3_eperl(1), wml_p4_gm4(1), wml_p5_divert(1), wml_p6_asubst(1), wml_p7_htmlfix(1), wml_p8_htmlstrip(1), wml_p9_slice(1).

wml::all(3)