Merge pull request #3973 from ericvergnaud/document-versioning-strategy

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Author: parrt

README.md

@@ -4,6 +4,17 @@
 [![License](https://img.shields.io/badge/license-BSD-blue.svg)](https://raw.githubusercontent.com/antlr/antlr4/master/LICENSE.txt)
 
 
+## Versioning
+
+ANTLR 4 supports 10 target languages, and ensuring consistency across these targets is a unique and highly valuable feature.
+To ensure proper support of this feature, each release of ANTLR is a complete release of the tool and the 10 runtimes, all with the same version.
+As such, ANTLR versioning does not strictly follow semver semantics:
+- a component may be released with the latest version number even though nothing has changed within that component since the previous release
+- major version is bumped only when new grammar features are released (such as ANTLR3 -> ANTLR4)
+- minor version updates may include minor breaking changes, the policy is to regenerate parsers with every release
+- backwards compatibility is only guaranteed for patch version bumps 
+If you use a semver verifier in your CI, you probably want to apply special rules for ANTLR, such as treating minor change as a major change.
+
 **ANTLR** (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files. It's widely used to build languages, tools, and frameworks. From a grammar, ANTLR generates a parser that can build parse trees and also generates a listener interface (or visitor) that makes it easy to respond to the recognition of phrases of interest.
 
 **Dev branch build status**