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README.md

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+# Fallback for `psr/http-message-implementation` using `nyholm`
+
+Provides a metapackage for library needing `psr/http-message-implementation` 
+that fallback to a default implementation when user does not meet
+the initial requirements.
+
+## Usage
+
+```shell
+composer require "Neur0toxine/psr.http-message-implementation.nyholm:*"
+```
+
+Composer will, by preference:
+- use an implementation provided by the user
+- otherwise, fallbacks to `nyholm/psr7`
+
+## How does it works
+
+This package contains 2 versions:
+
+1. The highest [1.1](https://github.com/Neur0toxine/psr.http-message-implementation.nyholm/blob/1.1/composer.json) needs nothing more than your requirements.
+
+1. The lowest [1.0](https://github.com/Neur0toxine/psr.http-message-implementation.nyholm/blob/1.0/composer.json) triggers install of `nyholm/psr7`.
+
+Composer will choose this highest version when user already has a package that satisfy `psr/http-message-implementation`.
+Otherwise, composer will choose the lowest version and in that case will 
+download the following packages: `nyholm/psr7`.
+
+## What problem does it solve?
+
+You are maintaining a library that need an implementation of `psr/http-message-implementation`,
+but you don't want requiring a specific implementation. 
+
+ie. You are maintainer of library that use the following composer.json
+```json
+{
+  "name": "acme/lib",
+  "require": {
+    "psr/http-message-implementation": "^1.0",
+  }
+}
+```
+
+When end users requires you library with the following code 
+```json
+{
+    "name": "end-user/app",
+    "require": {
+      "acme/lib": "^1.0"
+    }
+}
+```
+
+They probably ends with such error
+
+```shell
+composer up
+
+Your requirements could not be resolved to an installable set of packages.
+
+  Problem 1
+    - Installation request for acme/lib ^1.0 -> satisfiable by acme/lib[1.0].
+    - acme/lib 1.0 requires psr/http-message-implementation ^1.0 -> no matching package found.
+```
+
+You can ask user to install a random package, it works, but the DX is very bad,
+and confusing at first.
+
+By using `Neur0toxine/psr.http-message-implementation.nyholm`, 
+users will be able to require their preferred implementation 
+or fallback to your default choice
+
+### Example of user that meet the preferred requirements
+
+```json
+{
+    "name": "end-user/app",
+    "require": {
+        "acme/lib": "^1.0",
+        "third-party/provide-implementation": "^1.0"
+    }
+}
+```
+```shell
+composer up
+...
+Package operations: 2 installs, 0 updates, 0 removals
+  - Installing acme/lib (1.0)
+  - Installing Neur0toxine/psr.http-message-implementation.nyholm (1.1)
+```
+
+### Example of user that fallback to your recommendations
+
+```json
+{
+    "name": "end-user/app",
+    "require": {
+        "acme/lib": "^1.0"
+    }
+}
+```
+```shell
+composer up
+...
+Package operations: 3 installs, 0 updates, 0 removals
+  - Installing acme/lib (1.0)
+  - Installing Neur0toxine/psr.http-message-implementation.nyholm (1.0)
+  - Installing nyholm/psr7 (1.0)
+```
+
+## Contributing
+
+This repository is automatically generated. If you want contributing and 
+submitting an issue or a Pull Request, please use 
+[composer-fallback/generator](https://github.com/composer-fallback/generator).