Adoption tiers

xript is adopted incrementally. A host does not have to expose everything at once; it picks the tier that matches what it needs today and grows later. Each tier is a superset of the one before.

Tier 1 — expressions

The host evaluates user-supplied expressions in a sandbox. No bindings, no host calls — just safe evaluation of values. Use when the extensibility you need is “let users write a formula” and nothing more.

Tier 2 — simple bindings

The host exposes a set of bindings and lets mods call them. Mods are scripts that read host state and invoke host actions through the declared surface. Use when mods need to do things in the host but do not yet contribute UI.

Tier 3 — advanced scripting

Full scripting with hooks, capabilities, and lifecycle. Mods react to host events, request gated capabilities, and carry real behavior. Use when mods are first-class participants in how the application behaves.

Tier 4 — full feature

Everything, including UI contribution: slots, fragments, contributions, and the fragment protocol. Mods add and replace presentation, not just behavior. Use when the application is fully moddable and its own content is authored as mod zero.

Choosing a tier

Pick the lowest tier that covers what mods genuinely need now. Adding a higher tier later is additive — new bindings, hooks, slots, and capabilities extend the manifest without breaking existing mods. Do not expose tier 4 surfaces for a host whose mods only need tier 2; do not cap a host at tier 2 when its mods clearly want to contribute UI. The manifest grows with the need.