Caller entries are appended, so every built-in figure stays reachable, except
where a caller entry carries the id of a built-in: that one is a replacement
and takes the built-in's place, which is how a caller corrects a figure it
disagrees with rather than having both offered.
Merge a caller's dictionary into a built-in one.
Caller entries are appended, so every built-in figure stays reachable, except where a caller entry carries the id of a built-in: that one is a replacement and takes the built-in's place, which is how a caller corrects a figure it disagrees with rather than having both offered.