I received an email back from the developers of the plugin with the following information:
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Hi ewon,
I've never actually used pagerAnchorBuilder before now, but I just got it working with radSLIDE. It's just not the simplest to set up. For pagerAnchorBuilder to work, you also need to set a pager div. So, for example, if you want to put the slideshow on a page in wordpress, you have to edit that page, switch to HTML mode, and write something like this:
radslide 1
<div id="radslide-pager"></div>
Then when you're editing the settings of your slideshow, they need to look something like this:
{
timeout:2000,
speed:500,
pager: '#radslide-pager',
pagerAnchorBuilder: function(index, element){
return '<p>SLIDE '+index+'</p>';
}
}
So on your page you need to have an extra div to hold the pager items, and then in the radSLIDE settings you need to specify what the selector of that div is, and also specify how each individual slide should look inside the pagerAnchorBuilder function. Make sense?
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This only returns the numbers....