Update grammar docs

editions/tw5.com/tiddlers/dev/TiddlerFilter Formal Grammar.tid

@@ -1,10 +1,10 @@
 created: 20140210141217955
-modified: 20140210141312363
+modified: 20140303091312363
 tags: dev
 title: TiddlerFilter Formal Grammar
 type: text/vnd.tiddlywiki
 
-TiddlerFilters follow a formal grammar:
+TiddlerFilters follow a formal grammar that is presented here for users who are familiar with the notation. It isn't necessary to understand this grammar in order to write your own filter expressions.
 
 ''<filter-string>'' ::= ''<opt-whitespaces>'' ''<filter-operand>'' | ''<opt-whitespaces>'' ''<filter-operand>'' ''<filter-string>''