If this value is true, then a search box is added to the top of the persistent Table of Contents (ToC). Any string typed into this search box will be used to filter the entries shown below it.

The filter is a case-insensitive regular expression match against the text of each line in the ToC where arbitrary characters may occur anywhere in the string. In other words, the text “cat” will generate the regular expression “c.*a.*t.*” for the purpose of searching.

This setting has no effect if $persistent-toc is false.