YAML 1.2 Merge Key Precedence and Duplicate Key Handling

The YAML 1.2 specification introduces the merge key ! to facilitate map merging. However, the specification does not explicitly define precedence rules when a map contains multiple merge keys or when nested merges are applied.

This lack of a defined standard creates uncertainty during serialization and deserialization, particularly when attempting to maintain idempotent writes. Different parser implementations may resolve duplicate keys or merge order differently, leading to inconsistent data structures across different environments.

Technical Constraints

• Dependence on parser-specific behavior for merge key resolution.
• Risk of non-deterministic output when serializing documents with duplicate keys.
• Potential for duplicate node creation when using anchors and aliases without strict resolution.

Which behavior is considered the standard for merge key precedence when multiple aliases are merged into a single map? How do different YAML 1.2 compliant parsers typically resolve conflicts between duplicate keys during a merge operation?