I'm cutting a string for teasering out of a longer string. Works good. How can i avoid that if the string contains some HTML-Tags the cut does not happen inside a tag?

$input = 'Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores <a href="bla.html">Klick.</a> et ea rebum. Stet clita <a href="bla.html">Klick.</a> kasd gubergren, no sea takimata <a href="bla.html">Klick.</a> sanctus est Lorem ipsum dolor sit amet.'

$last_space = strrpos(substr($input, 0, $length), '.');
$trimmed_text = substr($input, 0, $last_space);