Merge pull request #38 from rdicosmo/main

Specify that qualifiers must occurr at most once.

Chapters/6.Qualified_identifiers.md

@@ -22,9 +22,12 @@ as detailed in the following sections.
 ## 6.1 Fragment qualifiers
 
 There are two fragment qualifiers, `lines` and `bytes`.
+Each fragment qualifier MUST appear at most once.
+
 Fragment qualifiers are only valid for objects of type content.
 
-The two fragment qualifiers are mutually exclusive: a valid SWHID MUST not contain both.
+Each valid SWHID must have at most one fragment qualifier.
+
 A conformant implementation MAY accept a SWHID that violates this constraint,
 by ignoring the `lines` qualifier when the `bytes` qualifier is present.
 
@@ -55,6 +58,9 @@ does not rely on any convention about line numbers.
 
 ## 6.2 Context qualifiers
 
+There are four context qualifiers, `origin`, `visit`, `path` and `anchor`.
+Each context qualifier MUST appear at most once.
+
 ### 6.2.1 Origin qualifier
 
 This qualifier allows to declare the *software origin* where the