$re = '/<assign.*?>/';
$str = '<if VERSION="A1" || VERSION="A3" || VERSION="a2_%5C%22A3">
<assign CTA="blue">
<assign CTA2="green">
<assign TEXT1="Hello%3Cbr/%3EWorld">
<elseif attribute-name="A2">
<assign CTA="red">
<assign CTA2="yellow">
<assign CTA3="brown">
<assign TEXT1="Click%20%3Ca%20href=\'https://example.com\'%20style=\'text-decoration:none;color:#000000;\'%3Ehere%3C/a%3E">
</if>
// condition 2
<if FOO_BAR="A4" || baz-biz="A5">
<assign CTA="purple">
<assign CTA2="orange">
<assign TEXT1="Hi%20%3Cspan%20style=\'font-%20weight:bold;\'%3EJohn%3C/span%3E" TEXT2="Hello%3Cbr/%3EWorld">
</if>
// condition 3
<if LANG="en_US">
<assign TITLE="English">
</if>';
$subst = "$&</assign>";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php