Why is it recommended to avoid using short tags like <? in PHP code, especially when upgrading to PHP 5.3?

Short tags like <? are not recommended because they may not be enabled by default in PHP configurations, causing compatibility issues when upgrading to newer versions like PHP 5.3. To ensure code portability and compatibility, it is best to use the full <?php tag for opening PHP code blocks. To fix this issue, simply replace all short tags with the full <?php tag in your PHP code.

// Before fix
<? echo "Hello, World!";

// After fix
<?php echo "Hello, World!";