Are you sure you are not thinking of the "Recovery" slider which used to be in earlier Camera raw conversion processes (specifically conversion process 1 and 2)

In process version 3 onwards ( current is 5) , Recovery is replaced with Highlights and Whites, which function differently but can achieve the same thing, recovering mildly blown highlights by using the info from channels which have not blown.

If you ever want to compare the different process, go to the calibration tab and choose from there. This of course also allows you to reprocess older raw images using the new process versions.
Dave