fix: disallow nested data-checkswipe

Handlers must be applied from bottom-up in order to get some effect of
nested groups that do not interact with each other. Even so, the CSS
enlarges all checkboxes, even if they "shouldn't"

checkswipe.js

@@ -14,6 +14,11 @@ function checkswipe(parent, checkbox) {
             return
         }
 
+        if (parent.parentElement?.closest('[data-checkswipe]') || parent.querySelector('[data-checkswipe]')) {
+            console.error('checkswipe: invalid structure for', parent,'; nested `data-checkswipe` elements are not allowed.')
+            return
+        }
+
         if (!(checkbox instanceof HTMLInputElement) || checkbox.type !== 'checkbox') {
             console.error('checkswipe: element', checkbox, `must be an html input element (type checkbox); is '${typeof checkbox}'.`)
             return
@@ -86,6 +91,11 @@ function checkswipe(parent, checkbox) {
             return
         }
 
+        if (group.parentElement?.closest('[data-checkswipe]') || group.querySelector('[data-checkswipe]')) {
+            console.error('checkswipe: invalid structure for', group,'; nested `data-checkswipe` elements are not allowed.')
+            return
+        }
+
         const hasSpecificCheckbox = group.querySelector('input[type=checkbox][data-checkswipe-use]') !== null
         if (hasSpecificCheckbox && group.dataset.checkswipeSpecify === undefined) {
             console.error('checkswipe: element', group, 'is missing attribute `data-checkswipe-specify`; has checkboxes with attribute `data-checkswipe-use`. this is not allowed.')