Update docs for "each" filter

editions/tw5.com/tiddlers/filters/each.tid

@@ -1,5 +1,5 @@
 created: 20140410103123179
-modified: 20170103175939836
+modified: 20191209085901849
 tags: [[Filter Operators]] [[Group Operators]]
 title: each Operator
 type: text/vnd.tiddlywiki
@@ -20,6 +20,6 @@ Each input title is processed in turn. The value of field <<.place F>> in the co
 ;each:value
 :As long as the title is unique it is appended to the output whether or not the corresponding tiddler exists.
 
-If a tiddler does not contain field <<.place F>>, it is treated as if the value of the field were empty.
+Note that if a tiddler does not contain field <<.place F>>, it is treated as if the value of the field were empty. Thus, a filter expression such as `[each[color]]` will return one tiddler that doesn't have a `color` field. To obtain just the tiddlers that have a non-blank value for the `color` field one can use `[each[color]has[color]]`.
 
 <<.operator-examples "each">>