What are potential reasons for a constant variable not being accessible after using ob_get_clean?

The issue may be due to the fact that ob_get_clean() not only returns the buffer content but also clears the output buffer. To access the content without clearing the buffer, you can use ob_get_contents() instead. This function returns the buffer content without removing it from the buffer.

ob_start();
echo "Hello, World!";
$content = ob_get_contents();
ob_end_clean();

// Now $content will hold the value "Hello, World!"