Extension for Boolean attributes

In the section describing Boolean attributes (3.3.4.2 in the 19990824
recommendation) suggests that:

> ... their appearance in the start tag of an element implies that the
> value of the attribute is "true". Their absence implies a value of
> "false".
>
> Boolean attributes may legally take a single value: the name
> of the attribute itself (e.g., selected="selected"). ...

For the next level of HTML (4.1?) why not allow boolean values to be
specified using a Boolean definition of 'true' and 'false'? This would be
a useful datatype which could be used in other locations as well.

It also allows the representation of future HTML elements which have a
default value of 'true' (rather than the default 'false' that selected et
al have)

<anElement>                 <!-- implicitly visible="true" -->
<anElement visible="false"> <!-- explicitly visible="false">

This could be declared similar to:

<!ENTITY % Boolean (true | false) "false" >

In this case, the elements defined for 'selected' etc could be written as:

<!ELEMENT OPTION>
<!ATTLIST OPTION selected %Boolean;>

Although it is too late to incorporate something like this into HTML4.0,
can it be considered/thought of for the next release of HTML/XHTML? It
would be easier to parse/recognise 'boolean' attributes using this
mechanism than the selected="selected" that is current, and it allows the
presence of some default-true values (such as visible) to be represented.

Alex Blewitt.

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Received on Wednesday, 6 October 1999 12:37:18 UTC