Thus, if I say, "Men who grasp after riches, are never satisfied;" the relative who is taken restrictively, and I am understood to speak only of the avaricious.
"The Grammar of English Grammars"
Goold Brown
Thus that and as are appropriately our restrictive relatives, though who and which are sometimes used restrictively; but, in a resumptive sense, who or which is required, and required even after those terms which usually demand that or as: thus, We are vexed at the unlucky chance, and go away dissatisfied.
"The Grammar of English Grammars"
Goold Brown