How can PHP developers ensure their code meets HTML validation standards?

PHP developers can ensure their code meets HTML validation standards by using PHP functions such as `htmlspecialchars()` to properly escape special characters in their output. This helps prevent HTML injection attacks and ensures that the generated HTML is valid. Additionally, developers should pay attention to the structure of their HTML code, making sure to close all tags properly and use semantic markup.

// Example of using htmlspecialchars() to escape special characters in PHP output
echo htmlspecialchars($variable);