Requirements.md

@@ -6,10 +6,21 @@ Discussion about this doc in #19
 
 This doc describe the whole process of invoicing in FreedomCoop. It should detail the workflows, user roles, user permissions, translations, etc. This is not a tech doc but a description about how the future apps should work and what features are a must, desired, or optionals.
 
-Customer: Organization or person invoiced. It receives the invoice and make a payment.
-Partner: FreedomCoop partner wich wants to make an invoice to Customer.
-Manager: FreedomCoop worker.
-Admin:   Supersuser, tech, issues, new features,...
+### Common vocabulary
+* Customer: Organization or person invoiced. It receives the invoice and make a payment.
+* Partner: FreedomCoop partner wich wants to make an invoice to Customer.
+* Manager: FreedomCoop worker.
+* Admin:   Supersuser, tech, issues, new features,...
+
+### Definitions
+
+RFC 2119 gives the following definitions:
+
+    MUST This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification.
+    MUST NOT This phrase, or the phrase "SHALL NOT", mean that the definition is an absolute prohibition of the specification.
+    SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.
+    SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label.
+    MAY This word, or the adjective "OPTIONAL", mean that an item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product while another vendor may omit the same item. An implementation which does not include a particular option MUST be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality. In the same vein an implementation which does include a particular option MUST be prepared to interoperate with another implementation which does not include the option (except, of course, for the feature the option provides.) 
 
 ## Workflow