According to Wikipedia this is indeed right.. https://en.wikipedia.org/wiki/Robots_exclusion_standard#Allow_directive Then there are only many wrong examples out there.
@@ -1,4 +1,4 @@
# Might as well keep robots away for performance and privacy reasons.
User-agent: *
-Disallow: /
Allow: /index.php
+Disallow: /
rugk