Clarify Environment Variable mapping

documentation/src/main/docs/config/environment-variables.md

@@ -1,6 +1,6 @@
 # Environment Variables
 
-Environment variable names follow the conversion rules specified by [MicroProfile Config](https://github.com/eclipse/microprofile-config/blob/master/spec/src/main/asciidoc/configsources.asciidoc#default-configsources).
+Environment Variable names follow the conversion rules specified by [MicroProfile Config](https://github.com/eclipse/microprofile-config/blob/master/spec/src/main/asciidoc/configsources.asciidoc#default-configsources).
 
 SmallRye Config specifies additional conversion rules:
 
@@ -13,22 +13,38 @@ with `_`: `FOO__BAR__BAZ`
 
 !!! danger
 
-    Environment variables format cannot represent the entire spectrum of common property names.
+    Environment Variables format cannot represent the entire spectrum of common property names.
 
-By default, the underscore `_` of an environment variable name always maps to a dot `.`. If the property name
-contains a dash or some other special character, that property name needs to be specified in one of the Config 
-sources. It will provide additional information to SmallRye Config on converting the environment variable name.
+The lookup of configuration values from Environment Variables will always use the dotted format name. For 
+instance, the lookup of the Environment Variable `FOO_BAR` value, requires the property name `foo.bar`:
+
+```java
+ConfigProvider.getConfig().getValue("foo.bar", String.class);
+```
+
+When SmallRyeConfig performs the lookup on the Environment Variables Config Source, it applies the conversion rules to 
+find the matching property name and retrieve the value. 
+
+In some situations, looking up the exact property name is impossible. For instance, when SmallRye Config has to look up 
+a configuration that is part of a `Map`, and the property name contains a dynamic segment (a `Map` key). In this case, 
+SmallRye Config relies upon each source's list of property names. These must be converted back to their most likely 
+dotted format for Environment Variables.
+
+By default, the underscore `_` of an Environment Variable name always maps to a dot `.`. If the property name
+contains a dash or some other special character, that property name can be specified in another Config 
+Source, with the expected dotted format. It will provide additional information to SmallRye Config to perform a 
+two-way conversion and match the property names.
 
 For instance:
 
-_Config A_
+**Config A**
 ```console
 FOO_BAR_BAZ=VALUE
 ```
 
 Will map to `foo.bar.baz` and value `value`.
 
-_Config B_
+**Config B**
 ```console
 FOO_BAR_BAZ=VALUE
 ```
@@ -37,3 +53,9 @@ foo.bar-baz=default
 ```
 
 Will map to `foo.bar-baz` and value `value`.
+
+!!! note
+
+The property name in dotted format needs to exist somewhere to provide this additional information. It can be set in a 
+low ordinal source, even without value. The Environment Variables source will override the value and map the correct 
+configuration name.