What fundamental knowledge about HTTP, web servers, and browsers is essential for writing web applications in PHP, especially when dealing with time-based output?

When dealing with time-based output in PHP web applications, it is essential to understand how HTTP headers, web servers, and browsers handle caching and refreshing content. By setting appropriate cache-control headers in your PHP scripts, you can ensure that time-sensitive data is always up to date when requested by the browser. 

<?php
// Set cache-control headers to prevent caching of time-based content
header("Cache-Control: no-cache, no-store, must-revalidate");
header("Pragma: no-cache");
header("Expires: 0");

// Output the current time
echo "Current time: " . date("Y-m-d H:i:s");
?>

Keywords

HTTP web servers browsers time-based output PHP

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