The graphic artist types don't need to concern themselves with any of that logic (if there were any on this project); they just need to know that the condition may be true, in which case a link may appear on the page.

I agree, I think. This turns out to be tricky. Consider the following page: 

A | B | C

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where A, B, and C are conditional links, and the vertical bars are visual separators. It's actually tricky to code this in HTML where A might exist, but B might not, and C might. Or for some other arbitrary combination. We usually encode this in a widget, which tests whether A, B, or C are rendered (see below), and then fills in with a separator. In bOP, it might look like: 
NavBar(' | ', ['TASK_A', 'TASK_B', 'TASK_C']);

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The NavBar widget's render function would looks something like this (not tested :-): 
sub render {
    my($self, $source, $buffer) = @_;
    my($sep) = $self->render_attribute('separator'. $source);
    my($need_sep) = 0;
    foreach my $w (@{$self->get('values')}) {
        my($b);
        $self->unsafe_render_value($w, $source, \$b);
        $$buffer .= ($need_sep++ ? $sep : '') . $$b
            if $$b;
    }
    return;
}

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This delegates the task of knowing how TASK_* is rendered to the widgets that know how to render tasks. In this case, it would be the Link() widget which looks up the permissions and the label based on the task name dynamically.

The question I have is how would this look in other template languages. And, where do the labels come from? How are permissions determined? Who evaluates if the current user's role and the role's authorized permissions.

That's where the "graphic designer" model breaks down. Either the designer has to know Perl to deal with the missing element problem, or the programmer has to work with the designer. There's no simple solution, but if the templating language doesn't offer ways to ask those questions (and most don't in my experience), you are left making things up as you go. That makes for funky websites where links lead to errors as opposed to using the meta data to ensure links don't get rendered unless you have the permission to execute them.

In reply to Re: Re: Separation of Presentation and Application/Business Logic by robnagler
in thread the trend of the presentation layer driving application logic by princepawn

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