add note (#1821)

_rules/button-non-empty-accessible-name-97a4e1.md

@@ -42,6 +42,8 @@ Each target element has an [accessible name][] that is not empty (`""`).
 
 ## Background
 
+This rule considers an exception for "image buttons" (i.e., `input` elements with a `type` [attribute value] of `image`). Image buttons failing this rule would fail [Success Criterion 4.1.2](https://www.w3.org/WAI/WCAG21/Understanding/name-role-value) and [Success Criterion 1.1.1](https://www.w3.org/WAI/WCAG21/Understanding/non-text-content) which is not part of the accessibility requirements for this rule.
+
 ### Related rules
 
 - [Image button has non-empty accessible name](https://act-rules.github.io/rules/59796f)