How can I get the tags for a headline in a clock report formula?

Question

I'd like to understand how to retrieve the tags for a headline that is being processed by a clock mode report formula. Suppose I have a clock report table defined like this.

#+BEGIN: clocktable :maxlevel 2 :scope nil :formula "$3='(headline-get-tags $1)::@2$3=string(\"Tags\")"                                                                       
#+END:  

I can define a simple formula that returns the length of the headline, but I have yet to find an easy way to find the tags associated with the headline.

(defun headline-get-tags (headline)
  "Return the tags for a headline"
  (length headline)) 

Is there a simple way to get the tags with a headline?

Answer 1

Clock tables support a :properties option:

#+BEGIN: clocktable :properties ("ALLTAGS")
#+END:

And it turns out that tags are available by the special property name ALLTAGS. Here are the others:

http://orgmode.org/manual/Special-properties.html#Special-properties