What is the difference between using single quotes and double quotes in PHP when including files?

When including files in PHP, using single quotes or double quotes can affect how variables and escape sequences are interpreted. When using single quotes, variables and escape sequences are not parsed and are treated as literal strings. When using double quotes, variables and escape sequences are parsed and replaced with their values. To ensure proper parsing of variables and escape sequences, it is recommended to use double quotes when including files in PHP.

// Using double quotes for proper parsing of variables and escape sequences
include "example.php";