Explain namespaced keywords

Paving the way for #139

src/language-basics.adoc

@@ -93,7 +93,6 @@ used in <<maps-section,map data structures>> to efficiently represent the keys.
 :foobar
 :2
 :?
-:foo/bar
 ----
 
 As you can see, the keywords are all prefixed with `:`, but this character is only part
@@ -108,6 +107,37 @@ or are unclear about anything in the following example; <<function-section,funct
 ;; => :foo
 ----
 
+===== Namespaced keywods
+
+When prefixing keywords with a double colon `::`, the keyword will be prepended by the name of the current namespace.
+Note that namespacing keywords affects equality comparisons.
+
+[source, clojure]
+---
+::foo
+;; => :cljs.user/foo
+
+(= ::foo :foo)
+;; => false
+---
+
+Another alternative is to include the namespace in the keyword literal, this is useful when creating namespaced keywords
+for other namespaces:
+
+[source, clojure]
+---
+:cljs.unraveled/foo
+;; => :cljs.unraveled/foo
+---
+
+The `keyword` function has an arity-2 variant where we can specify the namespace as the first parameter:
+
+[source, clojure]
+---
+(keyword "cljs.unraveled" "foo")
+;; => :cljs.unraveled/foo
+---
+
 
 ==== Symbols