TiddlyWiki has a special syntax for expressing filters. They can be used to select tiddlers for an operation, or to filter a set of tiddlers to add or remove members.
The mechanism is easiest to understand by first presenting some example filter strings:
* `HelloThere` - the single tiddler titled `HelloThere` (if it exists)
* `[[A Title With Several Words]]` - the single tiddler titled `A Title With Several Words` (if it exists)
* `[title[MyTiddler]]` - the single tiddler titled `MyTiddler` (if it exists)
* `HelloThere Introduction` - The tiddlers titled `HelloThere` and `Introduction` (if they exist)
* `[tag[important]]` - any tiddlers with the tag `important`
* `[!tag[important]]` - any tiddlers not with the tag `important`
* `[tag[important]sort[title]]` - any tiddlers with the tag `important` sorted by title
* `[tag[important]!sort[title]]` - any tiddlers with the tag `important` reverse sorted by title
* `[[one][two][three]tag[tom]]` - any of the tiddlers called `one`, `two` or `three` that exist and are tagged with tom`
* `[[one][two][three]] [tag[tom]]` - any of the tiddlers called `one`, `two` or `three` that exist, along with all of the source tiddlers that are tagged with `tom`
* `[tag[tom]] [tag[harry]] -[[one][two][three]]` - all tiddlers tagged either `tom` or `harry`, but excluding `one`, two` and `three`
* `[[MyTiddler]tags[]]` - all tiddlers being used as tags on the tiddler `MyTiddler`
* `[[MyTiddler]tagging[]]` - all tiddlers being tagged with `MyTiddler`
An operator can be negated with by preceding it with `!`, for example `[!tag[Tommy]]` selects the tiddlers that are not tagged with `Tommy`.
The operator defaults to `title` if omitted, so `[[HelloThere]]` is equivalent to `[title[HelloThere]]`. If there are no spaces in the title, then the double square brackets can also be omitted: `HelloThere`.
The operands available with the `is` operator are:
Operations can be preceded with `-` to negate their action, removing the selected tiddlers from the results. For example, `[tag[Tommy]] -HelloThere -[[Another One]]` selects all tiddlers tagged with `Tommy` except those titled `HelloThere` or `Another One`.
Operations can be preceded with `+` in order to make them apply to all of the current results, rather than the original source. For example, `[tag[Jeremy]] [tag[Tommy]] +[sort[title]]` selects the tiddlers tagged `Tommy` or `Jeremy`, and sorts them by the `title` field.
Filters are processed with the following elements: