Add PSR-3 meta document to include type upgrades.

Author: Crell

accepted/PSR-3-logger-interface-meta.md

@@ -0,0 +1,44 @@
+# Logger Meta Document
+
+## 1. Summary
+
+The logger interface defines a common interface for logging system messages from an application or library.
+
+This metadocument was written post-hoc, as PSR-3 was originally passed before meta-documents were standard practice.
+
+## 2. Design Decisions
+
+### Static log messages
+
+It is the intent of this specification that the message passed to a logging method always be a static value.  Any context-specific variability (such as a username, timestamp, or other information) should be provided via the `$context` array only, and the string should use a placeholder to reference it.
+
+The intent of this design is twofold.  One, the message is then readily available to translation systems to create localized versions of log messages.  Two, context-specific data may contain user input, and thus requires escaping.  That escaping will be necessarily different if the log message is stored in a database for later rendering in HTML, serialized to JSON, serialized to a syslog message string, etc.  It is the responsibility of the logging implementation to ensure that `$context` data that is shown to the user is appropriately escaped. 
+
+## 3. People
+
+### 3.1 Editor(s)
+
+* Jordi Boggiano
+
+## 4. Votes
+
+[Approval vote](https://groups.google.com/g/php-fig/c/d0yPC7jWPAE/m/rhexAfz2T_8J)
+
+## 5. Errata
+
+### 7.1 Type additions
+
+The 2.0 release of the `psr/log` package includes scalar parameter types.  The 3.0 release of the package includes return types.  This structure leverages PHP 7.2 covariance support to allow for a gradual upgrade process, but requires PHP 8.0 for type compatibility.
+
+Implementers MAY add return types to their own packages at their discretion, provided that:
+
+* the return types match those in the 3.0 package.
+* the implementation specifies a minimum PHP version of 8.0.0 or later.
+
+Implementers MAY add parameter types to their own packages in a new major release, either at the same time as adding return types or in a subsequent release, provided that:
+
+* the parameter 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/link": "^2.0 || ^3.0"` so as to exclude the untyped 1.0 version.
+
+Implementers are encouraged but not required to transition their packages toward the 3.0 version of the package at their earliest convenience.