Creating a function with single quotes

Hello,

This has me befuddled.  I am trying create a simple experiment, rather
new to SQL and I am running into an issue with single quotes.  All I can
find on creating a function states the procedure should be contained
within single quotes.  My problem comes when I want to use a textual
representation of an interval.

create function csd_interval(integer) returns interval as 
'BEGIN
RETURN $1 * interval '1 msec'
END;'
LANGUAGE 'plpgsql';

it always fails at the '1 msec' point.

Suggestions?
-- 
Sincerely,

Shawn Tayler
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