The double quotes in PHP parse through the string for things like escape sequences and special characters (e.g., tab and newline). From there, they are replaced with their respective values.

The single quotes in PHP does not parse through the string for thigs like like escape sequences and special characters. So, everything inside single quotes are treated as literal. This means that the any escape sequences or special characters (e.g., tab and newline) are not processed and printed as is.