Lateral search example for Groups section

[benjwadams]

Question

Hi, could a non-trivial example be given for the "lateral search" that is used by CF for coordinate variables in groups?

https://cfconventions.org/cf-conventions/cf-conventions.html#_search_by_proximity

A special case exists for coordinate variables. Because coordinate variables must share dimensions with the variables that reference them, the ancestor search is executed only until the local apex group is reached. For coordinate variables that are not found in the referring group or its ancestors, a further strategy is provided, called lateral search. The lateral search proceeds downwards from the local apex group width-wise through each level of groups until the sought coordinate is found. The lateral search algorithm may only be used for NUG coordinate variables; it shall not be used for auxiliary coordinate variables.

[benjwadams]

This groups section could benefit from some tree diagrams illustrating the various cases.

The term "apex group" is not defined in the groups section, and the definition resides in the glossary.