Errata: Type additions

Author: navarr

accepted/PSR-16-simple-cache-meta.md

@@ -68,3 +68,26 @@ For being an early reviewer
 * [Survey of existing cache implementations][1], by @dragoonis
 
 [1]: https://docs.google.com/spreadsheet/ccc?key=0Ak2JdGialLildEM2UjlOdnA4ekg3R1Bfeng5eGlZc1E#gid=0
+
+## 8. Errata
+### 8.1 Type additions
+
+The 1.1 and 1.2 releases of the `psr/simple-cache` package includs scalar parameter types and increases the minimum PHP version to 7.2 and 8.0 respectively.  This is considered a backwards compatible change as PHP 7.2 introduces covariance for parameters.  Any implementation of 1.0 is compatible with 1.1 and 1.2.
+
+The 2.0 release includes return types.  Return types break backwards compatibility as PHP does not support return type covariance.  Implementations of 2.0 remain compatible with clients designed for 1.0.
+
+Implementers MAY add return types to their own packages at their discretion, provided that:
+
+* the return types match those in the 2.0 package.
+* the implementation specifies a minimum PHP version of 8.0.0 or later
+* the implementation depends on `"psr/simple-cache": "^1.2 || ^2"` so as to exclude the untyped 1.0 version.
+
+Implementers MAY add parameter types to their own package in a new minor release, either at the same time as adding return types or in a subsequent release, provided that:
+
+* the parameter types match or widen those in the 1.2 package
+* the implementation specifies a minimum PHP version of 7.2.0 (8.0 if using mixed or union types) or later.
+* the implementation depends on `"psr/simple-cache": "^1.1 || ^2"` so as to exclude the untyped 1.0 version. (`"psr/simple-cache": "^1.2 || ^2"` if using mixed or union types)
+
+Implementers are encouraged, but not required to transition their packages toward the 2.0 version of the package at their earliest convenience.
+
+Consumers are encouraged to update their requirement to `"psr/simple-cache": "^1 || ^2"` at their earliest convenience.