+// headers: an associative array; the values can take several forms
+// simple/legacy form is "label"=>"type"
+// more advanced form is "label"=>options, it self a dict with the following known keys
+// (*) 'type': the type for sorting; this is passed to the javascript layer for custom sorting
+// default is to use 'text', custom sort functions can be specified with e.g. 'type'=>'sortAlphaNumericBottom'
+// a special case is for type to be 'date-format' like e.g. 'type'=>'date-dmy'
+// setting type to 'none' gives an non-sortable column
+// (*) 'title': if set, this is used in the "Sort on ``<title>''" bubble