Known boundaries

Known Boundaries (KB-NNN) are declared behavior limits relative to the PLCopen specifications or the frozen v0.x implementation. They are part of the contract, not an informal bug list.

How to use the registry

1. Search the registry for the function block, subsystem, or KB-NNN referenced by code, tests, an issue, or a release note.
2. Read the matching semantic matrix in doc/compliance/.
3. Check the tests named by that matrix before changing the behavior.
4. If a cyclic output intentionally changes, update the KB entry and replay baseline in the same change.

The full append-only registry is the canonical known-boundaries document.

What the registry covers

• Function-block input combinations and unsupported modes.
• Command ownership, buffering, blending, and takeover behavior.
• Software-only claims that do not establish hardware truth.
• Real-time and allocation boundaries.
• Compatibility differences between the new kernel and the frozen legacy line.

What a boundary means

A boundary may describe a deliberate product limit, a standards gap, or a behavior that needs external hardware evidence. It does not automatically mean the implementation is defective. Conversely, the absence of a KB entry does not create a new guarantee beyond the documented API and semantic matrices.