I was going to +1 - I like Kito's idea of using a component author-specified attribute, and I also like Dan's idea of a more generic "strict" attribute - though then it occurred to me that the arbitrary attribute behavior isn't just a feature of Facelets compositions - but this is also the way that Facelets works for any old (Java-based) Faces component. That is, I believe that:

<h:commandButton foo="bar">

Just ends up stashing the "foo" attribute value in the <h:commandButton>'s attribute map. (Or, at least, I think that's what happens.) So now I am wondering whether there is merit in keeping behavior consistent between composite and non-composite components in this regard. Would it be confusing that arbitrary attributes are pushed into the attribute map for some types of components, but not for others? Hmm... maybe the benefits of providing quick feedback in cases where the attribute is known to be invalid (ie. in the composite component "strict" case) outweigh the drawbacks of the inconsistency?

If we do go forward with a strict capability for composite components, do we want to check/enforce this in all project stages? Seems like we might be able to get away with only performing the strict checks in the development project stage (sort of like disabling assertions for production releases).

Andy

Dan Allen wrote On 4/2/2009 2:34 PM ET:

Makes sense to me. One of the things I have always been uneasy about with Facelets is the amorphous aspect of the tags. So when it comes to defining a real component, I think we absolutely want the component author to be able to decide whether to make the tag strict or not.

Would a more generic attribute like strict="true" make more sense just in case we want to enforce other restrictions?

-Dan

On Thu, Apr 2, 2009 at 7:56 AM, Kito Mann <kito.mann@virtua.com> wrote:

So, here's one other thing that came up at JSFDays -- the fact that composite components (like Facelet compositions) don't restrict which attributes can be used. This is fine for Facelet compositions, but since composite components can define specific attributes, it makes sense to give component authors the ability to restrict page authors to those attributes.

I think the easiest way to handle this from a component author's perspective would be to add an attribute to the <component:interface> tag:

<component:interface restrictAttributes="true">
<component:attribute name="name" required="true"/>
<component:attribute name="size"/>
</component:interface>

So, in this case, this component would _only_ accept the name and size attributes, and the runtime would throw an exception if another attribute were used. An IDE could also complain when someone tried to use a different attribute.

Thoughts?
---
Kito D. Mann -- Author, JavaServer Faces in Action
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--
Dan Allen
Senior Software Engineer, Red Hat | Author of Seam in Action

http://mojavelinux.com
http://mojavelinux.com/seaminaction

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