Check single-occurrence in source code with PHP Codeception acceptance test

How can I check that a specific $string (f.e. 123) only occurs within a specific HTML element but not outside or anywhere else using PHP/Codeception acceptance tests?

Example which would be fine:

<html><body>foobar 234<div id="original">123</div></body></html>

Example which should fail #1 (text occurrence):

<html><body>foobar 123<div id="original">123</div></body></html>

Example which should fail #2 (link occurrence):

<html>
  <body>
    foobar
    <div id="original">123</div>
    <a href="/link/123">Link</a>
  </body>
</html>

What I've tried on tests other than that specific page:

$I->seeInPageSource($alias);
$I->dontSeeInPageSource($original);

Now I would need something like

$I->seeInPageSourceElement($original, '#original');

$I->dontSeeInPageSourceExceptElement($original, '#original');
// could be implemented like this:
$pageSourceWithoutElement = str_replace(
  $I->grabPageSourceElement('#original'),
  '',
  $I->grabPageSource()
);
$I->assertNotContains($original, $pageSourceWithoutElement);

Reason: I have two versions, where one version is alias for another (called "original"). I want to make sure only the alias is used everywhere except on the "show original" page, where the alias defition is shown.

Solution

I found a solution:

detach element with jQuery (requires the test page to use it)
do regular test
re-attach element

Not the perfect solution, but it works.

    public function dontSeeInPageSourceExceptElement($text, $excludeSelector)
    {
        $I = $this;

        // check for positive occurrence in exclude selector (optional)
        // $I->see($text, $excludeSelector);

        // detach the selected element
        // Problem: append() just re-attaches the element, but this might not be the right position
        $I->executeJs(
            sprintf(
                // s = subject, p = parent, bs = backup of subject
                "var s = $(%s), p = s.parent(), bs = s.detach(); " .
                "setTimeout(function() { p.append(bs); }, 2000);",
                json_encode($excludeSelector)
            )
        );

        // check for negative occurrence now
        $I->dontSeeInPageSource($text);

        // wait 2 seconds (re-attach timeout)
        $I->wait(2);
    }