Clarify Step Documentation
Clarify Step Documentation

While the redesign is in progress (#62886), clarify the purpose of replace_zero and replace_one.
graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust