title: FILTER_SANITIZE_STRING is stripping the < character and any text after it
body: <p>I have a strange problem when using <code>FILTER_SANITIZE_STRING</code> on a variable (populated by human input). It seems to strip the <code>&lt;</code> character and any text that comes after that. The <code>&gt;</code> character is left untouched.</p>
  
  <p>I assume it thinks the <code>&lt;</code> is an HTML tag that needs to be stripped, however there is no closing tag behind it, so I haven't got a clue why it would behave like that. Is there a way to make it leave the <code>&lt;</code> in place, and still sanitize the way it should? </p>