# Invariant Doc Entity
### Scope
- **Purpose**: Document the behavioral contracts and constraints all collection macros must uphold.
- **Responsibility**: Registry and overview of all invariant doc instances.
- **In Scope**: No-std allocation selection; compile-time capacity pre-allocation.
- **Out of Scope**: API signatures (see `api/`), feature guides (see `feature/`).
### Overview Table
| 001 | [No-std Allocation Selection](001_no_std_alloc.md) | HashMap/HashSet source switches between hashbrown and std based on feature flags | ✅ |
| 002 | [Capacity Pre-allocation](002_capacity_preallocated.md) | The 10 macros for capacity-supporting types pre-allocate exact capacity at compile time | ✅ |