Nuances of Comparing Data Types in PHP

Pay attention to the following code:

php<?php
  if (0 == '') {
    echo '+++';
  } else {
    echo '---'; // this will execute
  }
?>

And to the following:

php<?php
  if (0 == '0') {
    echo '+++'; // this will execute
  } else {
    echo '---';
  }
?>