Rules first
The rule translator reads the common string operations, such as lower case, substring, replace, join and a condition, renames each attribute through the provider tables and writes the result in the destination's own form. That is what this page shows.
A confidence you can read
100 means the rules are certain. 90 means the two languages differ on an edge case, and the note says which. 50 means an attribute has no known name on the destination, so a person checks it.
A reviewer decides
When the rules cannot express a claim, the review says so with the reason and offers suggestions for complex transformations. Nothing migrates until a person has approved the mapping.