So instead of using what I thought would be the id set in my div, I found in Dev Tools that it's actually something different. The following at least gives me a reference...
registry.byId('dijit_layout_ContentPane_1')
// but
registry.byId('dijit_layout_ContentPane_1').set('disabled',true);
// does nothing
If I try what has been suggested elsewhere, e.g. here, I get an error:
dojo.style(registry.byId('dijit_layout_ContentPane_1').controlButton.domNode,{display:"none"});
dojo.style(registry.byId('dijit_layout_ContentPane_1').controlButton.domNode,{display:"inline-block"});
>>TypeError: Cannot read property 'domNode' of undefined
What is this controlButton property? Why is it not available?