Document convention to use version 0 for alpha/beta kernels (#639)

Author: danieldk

docs/source/basic-usage.md

@@ -30,6 +30,11 @@ for older PyTorch versions. This ensures that your code will continue to work.
 
 Hub kernels must be loaded with either a `version` or an explicit `revision`.
 
+> [!NOTE]
+> Version `0` kernels are excluded from the API compatibility requirement,
+> since it is used for alpha/beta-quality kernels that may still have
+> rapidly changing APIs.
+
 ## Checking Kernel Availability
 
 You can check if a particular version of a kernel supports the environment
@@ -43,7 +48,7 @@ is_available = has_kernel("kernels-community/activation", version=1)
 print(f"Kernel available: {is_available}")
 ```
 
-When no compatible kernel is found, [`~kernels.has_kernel`] does not say *why*.
+When no compatible kernel is found, [`~kernels.has_kernel`] does not say _why_.
 [`~kernels.get_kernel_variants`] returns the full resolution trace instead: one
 decision per build variant in the repository, with compatible variants listed
 first. Each decision is a `VariantAccepted` or a `VariantRejected`, and rejected

docs/source/kernel-requirements.md

@@ -199,6 +199,12 @@ The version **must** be bumped in the following cases:
 In both cases, build variants that are not updated must be removed from
 the new version's branch.
 
+> [!NOTE]
+> By convention, we reserve version `0` for kernels that are still in
+> alpha or beta stage and are not recommended for production use (e.g.
+> because the API is still changing regularly or there are still too
+> many issues).
+
 ## Native Python module
 
 Kernels will typically contain a native Python module with precompiled

docs/source/layers.md

@@ -180,6 +180,11 @@ work.
 Hub-backed [`~kernels.LayerRepository`] and [`~kernels.FuncRepository`] entries must specify
 either a `version` or an explicit `revision`.
 
+> [!NOTE]
+> Version `0` kernels are excluded from the API compatibility requirement,
+> since it is used for alpha/beta-quality kernels that may still have
+> rapidly changing APIs.
+
 You can register a mapping, like the one above, using [`~kernels.register_kernel_mapping`]:
 
 ```python

docs/source/migration.md

@@ -14,6 +14,11 @@ for never breaking a kernel within a major version and should bump up
 the major version if the kernel API changes and/or when support for
 older Torch versions is removed.
 
+> [!NOTE]
+> Version `0` kernels are excluded from the API compatibility requirement,
+> since it is used for alpha/beta-quality kernels that may still have
+> rapidly changing APIs.
+
 You can find the versions that are supported by a kernel using the
 `kernels versions command`. For example: