introduce top-level name

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

schema/compose-spec.json

@@ -8,7 +8,12 @@
   "properties": {
     "version": {
       "type": "string",
-      "description": "Version of the Compose specification used. Tools not implementing required version MUST reject the configuration file."
+      "description": "declared for backward compatibility, ignored."
+    },
+
+    "name": {
+      "type": "string",
+      "description": "define the Compose project name, until user defines one explicitly."
     },
 
     "services": {

spec.md

@@ -49,6 +49,8 @@ A **Project** is an individual deployment of an application specification on a p
 resources together and isolate them from other applications or other installation of the same Compose specified application with distinct parameters. A Compose implementation creating resources on a platform MUST prefix resource names by project and
 set the label `com.docker.compose.project`.
 
+Project name can be set explicitely by top-level `name` attribute. Compose implementation MUST offer a way for user to set a custom project name and override this name, so that the same `compose.yaml` file can be deployed twice on the same infrastructure, without changes, by just passing a distinct name.
+
 ### Illustrative example
 
 The following example illustrates Compose specification concepts with a concrete example application. The example is non-normative.
@@ -223,6 +225,12 @@ Compose implementations SHOULD validate whether they can fully parse the Compose
 because the Compose file was written with fields defined by a newer version of the specification, Compose implementations
 SHOULD warn the user. Compose implementations MAY offer options to ignore unknown fields (as defined by ["loose"](#Requirements-and-optional-attributes) mode).
 
+## Name top-level element
+
+Top-level `name` property is defined by the specification as project name to be used if user don't se one explicitly. 
+Compose implementations MUST offer a way for user to override this name, and SHOULD define a mechanism to compute a
+default project name, to be used only if the top-level `name` element is not set.
+
 ## Services top-level element
 
 A Service is an abstract definition of a computing resource within an application which can be scaled/replaced