Talk about identifiers

Author: moritz

lib/Language/syntax.pod

@@ -128,7 +128,28 @@ of comment
 say 'code again';
 =end code
 
-=comment TODO: identifiers
+=head2 Identifiers
+
+Identifiers are a grammatical building block that occur in several places. An
+identifier is a primitive name, and must start with an alphabetic character
+(or an underscore), followed by zero or more word characters (alphabetic,
+underscore or letter). You can also join two or more identifiers by a dash
+C<-> or a single quote C<'>, and the result is also considered to be an
+identifier.
+
+    # valid identifiers:
+    x
+    something-longer
+    with-numbers1234
+    don't
+
+    # not valid identifiers:
+    with-nubmers1234-5
+    42
+
+Names of constants, types and routines are identifiers, and they also appear
+in variable names (optionally proceeded by a sigil; see
+L</language/variables|variables> for more details.)
 
 =head1 Statements and Expressions