destination(string) Name of variable where output will be stored.

needle(string) What you are replacing for. May be a PHP variable (formatted with the leading dollar sign$) containing the needle.

replacement(string) What you are replacing with. May be a PHP formatted variable containing the replacement.

haystack(string) Name of variable where the needle can be found.

This shortcode lods the haystack with the needle, replaces the needle in the haystack and then loads the resulting haystack into the destination variable.