Development plan

Current status (implemented in the 0.1.x line)

• stable element metadata
• curated covalent, van der Waals, and atomic-radius support datasets
• explicit provenance and coverage metadata
• generic value-policy core plus radii and X–H convenience wrappers
• substitution and linear transfer
• custom element-indexed scalar sets
• policy-backed transfer sources
• nested-policy safeguards, transfer-depth tracking, and cycle detection
• provisional X–H support via csd_legacy_xh_cno, XHPolicy, and DEFAULT_XH_POLICY

Planned for 0.2.x

• broader X–H datasets and policies
• experimental plus computational support sets
• pairwise helper logic such as reference sums and normalization schemes
• restoration of incomplete experimental data from broader-support predictors

Longer-term design ideas

• radial atomic reference functions
• simple proto-density support based on spherically averaged atomic data

Possible future directions

• more radii sets
• uncertainty and confidence flags
• ion-specific or atom-type-specific domains
• density-derived radii and related reference transforms