Excuse me for the misunderstanding. As far as I understand, you would like to replace the default arrow icon of the collapsible element with a different one. Is this correct? If you want to change the toggle down and up icons, you can set it with the attributes as you have stated in your reply:
Without having to add the icon's HTML inside the container as well. I have updated the Dojo you have sent me with an implementation of the example:
However, if you would like to add other icons as well, I am afraid this is currently not possible, as all of the icons within the collapsible container are being replaced with the icons specified in the expand and collapse attributes.
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