Single versus Double quote marks as string delimiters

Hi All,

I have heard other people say that PHP can parse double quoted strings
(e.g., "Hello, World") faster than it can parse single quoted strings (e.g.,
'Hello, World'). This seems backwards to me, since double quote strings
have to be checked for any variables that need to be interpreted, whereas
single quoted strings do not.

So, what is the truth on this matter? And the explanation? Thanks for any
information!

-Josh