1. Switch from using the text field of lists for storing the associated
filter to using the field `toc-list-filter` (to make it harder to
accidentally parse the text of an ordinary tiddler as a filter)
2. Fix several bugs
The exclude filter `+[tag[intro]]` will produce a document that only
includes the paragraphs with the tag “intro”. These are derived from
the paragraphs in the original document with the CSS class “intro”.
