Re: [wml] Handling unknown attributes

[Denis Barbier <nospam@thanx>]

On Sun, Jul 09, 2000 at 12:40:48AM +0200, Denis Barbier wrote:

[...]
> Mp4h version 1.0.4 introduces 3 new tags to play with attributes:
>    <attributes-remove name1,name2,... %attributes>
>       Like %attributes, but remove variables whose name is one of
>       name1, name2, and so on.
>    <attributes-extract name1,name2,... %attributes>
>       Prints only the name=value pair matching names name1, name2,...
>    <attributes-quotes %attributes>
>       The two macros above gobble quotes like any other mp4h macros.
>       This one prints its attributes with value between quotes. It must
>       only be used when printing its content on output without any
>       further processing.
[...]
> Next step is to add an `image' attribute:
>   <define-tag hyperlink whitespace=delete>
>   <preserve url text image>
>   <set-var <attributes-extract url,text,image %attributes>>
>   <defvar text "<get-var url>">
>   <a <attributes-quote <attributes-remove url,text,image %attributes>> \
>      href="<get-var url>">
>   <if <get-var image>
>       <img src="<get-var image>" alt="<get-var text>">
>       <get-var text>>
>   </a>
>   <restore  url text image>
>   </define-tag>
>   <hyperlink url="http://..." class=www image=foo.gif>
> 
> But there is a trivial flaw in this implementation, we have to choose if
> unknown attributes go into <a> or <img>.

What do you think of this writing?

  <define-tag hyperlink whitespace=delete>
  <preserve url text image>
  <set-var <attributes-extract url,text,image %attributes>>
  <a <attributes-quote <attributes-extract :a:(.*) %attributes>> \
     href="<get-var url>">
  <if <get-var image>
     <img <attributes-quote <attributes-extract :img:(.*) %attributes>> \
        src="<get-var image>" alt="<get-var text>">
     <get-var text>
  >
  </a>
  <restore  url text image>
  </define-tag>
  <hyperlink :a:class=web :img:id=logo :img:border=1 \
      url="http://www.foo.com" text="Welcome" image="foo.png">

prints

  <a class="web" href="http://www.foo.com"><img id="logo" border="1"
  src="foo.png" alt="Welcome"></a>


Wildcards are allowed in first argument of <attributes-*>, and when
there is a subexpression, it is printed instead of the whole expression.

-- 
Denis Barbier
WML Maintainer
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