One of the things TiddlyWiki does best is selecting tiddlers that match certain criteria and remixing them into different forms. This chapter explores these capabilities in two phases.

1. We'll learn how to write filters to choose tiddlers that match almost any criteria you can think of.
2. We'll take a deeper dive into wikitext by learning the basics of the formatting language HTML and its TiddlyWiki extensions, which we will continue to use throughout the rest of the book.

At the end, we'll bring these topics together by creating formatted lists of tiddlers that automatically update to match the results of a filter, and we'll discuss some troubleshooting skills to be used when these features don't work as expected.

In this chapter

• Filters – Filters are a lightweight query language used primarily to select tiddlers.
• Using Filter Expressions – Filter expressions, runs, and steps work together to select tiddlers.
• Anatomy of Filter Steps – Filter steps have operators, suffixes, parameters, inputs, and outputs.
• Common Filter Operators – A small number of basic filter operators will handle many of your common needs.
• HTML – HTML is a simple formatting language used to describe web pages, including TiddlyWikis. We can go “down a level” from wikitext to HTML when we need a bit more control over presentation.
• Widgets – Widgets are a TiddlyWiki extension to HTML exposing wiki-specific functionality.
• Your First Dynamic List – You can create lists of tiddlers that automatically update to show all the tiddlers that currently match a filter.
• Comments – You can leave notes to yourself in your wikitext that don't appear in the output.
• When Things Go Wrong – As your wikitext gets more complicated, it occasionally might not do what you were expecting; here's how you can figure out what you did wrong.