docs(template-no-unsupported-role-attributes): document specificity heuristic

The "pick entry with most attribute constraints satisfied" resolution is a
heuristic, not a spec-documented approach. aria-query's elementRoles is an
unordered Map; aria-query does not publish a resolution order for
multi-match cases. Name the inference, cite the motivating bug cases, and
note that if aria-query ever publishes resolution semantics we should
switch to those.

Author: johanrd

lib/rules/template-no-unsupported-role-attributes.js

@@ -52,6 +52,16 @@ function getImplicitRole(node) {
   // Each elementRoles entry lists attributes that must match (with optional
   // constraints "set" / "undefined"); pick the most specific entry whose
   // attribute spec is fully satisfied by the node.
+  //
+  // Heuristic: "specificity = attribute-constraint count". aria-query exports
+  // elementRoles as an unordered Map and does not document how consumers
+  // should resolve multi-match cases; this count-based tiebreak is an
+  // inference from the data shape. It resolves the motivating bugs:
+  //   - <input type="text"> without `list` → textbox, not combobox
+  //     (the combobox entry requires `list=set`, a stricter 2-attr match;
+  //     the textbox entry's 1-attr type=text wins when `list` is absent).
+  //   - <input type="password"> → no role (no elementRoles entry matches).
+  // If aria-query ever publishes a resolution order, switch to that.
   let bestKey;
   let bestSpecificity = -1;
   for (const key of elementRoles.keys()) {