IMHO, i would be very useful to be able to customise the toggle indicator a little bit more. Something like the img directive parameters would be appreciated:

You can also pass alt, title, class, align, id, hspace, and vspace parameters. These are passed through unchanged to the html img tag. If you include a caption parameter, the caption will be displayed centered beneath the image.

So that for instance:

 [[!toggle  id="toggleable-id" text="Toggle" class="collapser"]]

could produce:

 <a class="toggle collapser" href="#posts.toggleable-id">Toggle</a>

This could be extra-useful when using icons like Font Awesome so that the toggle link could be a nice icon instead of text.

-- Hugo