-EXPRESSION = '"' ( ECHAR | '{' VARNAME '}' )* '"' | re"'[^'\\n]*'" | VARNAME
-ECHAR = re('([^\\{}]|\\\\|\\{|\\}|\\n)*')
-VARNAME = re('[a-zA-Z0-9-_]+(\.[a-zA-Z0-9-_]+)*')
+.. todo:: should whitespace (incl. '\n') be allowed (almost) everywhere?
+ can comment be anywhere whitespace can?
+.. note:: ';' or '\n' is currently required even after CONDITION and SUBTREE block
+.. todo:: change to OPERATION only
+.. note:: Formula can contain additional/unnecessary parentheses