2014-06-08: Improve SRFI thanks to the comment from Alan.

Improve SRFI thanks to the comment from Alan.

diff --git a/docs/srfi.org b/docs/srfi.org
--- a/docs/srfi.org
+++ b/docs/srfi.org
@@ -297,6 +297,7 @@ The syntax shown here is the minimal syn
         string-append "Hello " who "!"    ;        (string-append "Hello " who "!")))
 #+END_SRC
 
+If the colon starts a line, it starts a bracket which gets closed at the end of the line *and* defines an indentation level at the position of the colon.
      
 ***    *You can replace any number of consecutive initial spaces by underscores*, as long as at least one whitespace is left between the underscores and any following character. You can escape initial underscores by prefixing the first one with \ ("\___ a" → "(___ a)"), if you have to use them as function names.
 
@@ -313,6 +314,8 @@ The syntax shown here is the minimal syn
 
 - square brackets and curly braces should be treated the same way as parentheses: They stop the indentation processing until they are closed.
 
+- : at the beginning of a line adds an extra open parentheses that gets closed at end-of-line (rule 4.2.7) *and* defines an indentation level.
+
 ** Syntax justification
 
 /I do not like adding any unnecessary syntax element to lisp. So I want to show explicitely why the syntax elements are required./