What are some debugging techniques to identify the source of the error "cannot modify header information - headers already sent by" in PHP?

The error "cannot modify header information - headers already sent by" in PHP occurs when there is output sent to the browser before PHP sends headers. To solve this issue, make sure there is no whitespace or any output (including HTML, text, or even a BOM) before the `header()` function is called. 

<?php
ob_start(); // Start output buffering

// Your PHP code here

ob_end_clean(); // Clean the output buffer
header("Location: newpage.php"); // Redirect to new page
exit(); // Ensure no further code is executed after the header redirect
?>

Keywords

PHP debugging techniques headers error modification

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