What are the differences between using single quotes and double quotes in PHP when generating HTML content?

When generating HTML content in PHP, using double quotes allows for the interpolation of variables and special characters, while single quotes treat everything as a literal string. This means that using double quotes can make it easier to include variables within the HTML content without concatenation. However, when performance is a concern, single quotes may be preferred as they are slightly faster than double quotes.

// Using double quotes to interpolate variables in HTML content
$name = "John";
echo "<p>Hello, $name!</p>";

// Using single quotes for literal strings in HTML content
echo '<p>Hello, ' . $name . '!</p>';