strpos() returns false when needle string contains an invisible / zero-width character

Question

Why it is not returning good?

<?php
$r = "<h3>Welcome</h3>";
if (strpos($r, "​Welcome") !== FALSE) {
    echo "Good";
}
?>

Reproduce by hardcoding the offending unicode character which was destroyed when creating this post:

$r = "<h3>Welcome</h3>";
if (strpos($r, "\u{200C}Welcome") !== FALSE) {
    echo "Good";
}

Answer 1

Do you see the little ​ box? That is E2 80 8B in UTF-8, the zero-width space.
And that's not present in your source text.

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