What are common issues when outputting content from applications in PHP?

One common issue when outputting content from applications in PHP is the presence of whitespace before the opening `<?php` tag or after the closing `?>` tag, which can cause headers to be sent prematurely and lead to errors. To solve this, ensure that there is no whitespace before the opening `<?php` tag and avoid using the closing `?>` tag at the end of PHP files.

<?php
// Correct way to output content in PHP without whitespace issues
echo "Hello, World!";