Contents.StringContents of type string, with the default 3-way merge strategy: assume that update operations are idempotent and conflict iff values are modified concurrently.
Merge function. Evaluates to `Conflict msg if the values cannot be merged properly. The arguments of the merge function can take None to mean that the key does not exists for either the least-common ancestor or one of the two merging points. The merge function returns None when the key's value should be deleted.