Filter operators are used to select tiddlers based on some criteria. For example, this filter consists of a single operation that selects all tiddlers tagged "introduction":
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`.
Filter operations can be negated by preceding the operator with an exclamation mark (!). This example selects all tiddlers that are not tagged "introduction":
```
[!tag[introduction]]
```
! Operator Suffixes
Some filter operators can take an optional suffix that provides further information for the operation. For example, the "field" operator takes a suffix indicating the field to be compared. The following filter returns all tiddlers that have "JeremyRuston" in the "modifier" field:
If an unknown operator is used then it is instead interpreted as the suffix of the "field" operator. Thus, these two filters both return all the tiddlers that contain the string "create" in their "caption" field:
If a filter operator is written with curly brackets around the operand then it is taken to be a TextReference to the actual value. For example, this filter selects all tiddlers containing the string contained in the tiddler titled "$:/temp/search"
If a filter operator is written with angle brackets around the operand then it is taken to be the name of a variable containing the actual value. For example, this filter selects all tiddlers containing the title of the current tiddler:
```
[search<currentTiddler>]
```
(Note that the `currentTiddler` variable is used to track the current tiddler).
A sequence of operators can be logically ANDed together by bashing them together and merging the outer square brackets. This is called a "run" of operations. For example, here we select tiddlers that are tagged "introduction" and also tagged "demo":
Ordinarily, each run of filter operations adds to the accumulated results. Prefixing a run with `-` causes the list of tiddlers to instead be removed from the results. For example, this example returns all the tiddlers tagged "introduction" apart from `HelloThere` and `Title with Spaces`:
[tag[introduction]] -HelloThere -[[Title with Spaces]]
```
This example returns all tiddlers tagged "introduction" that are not also tagged "demo":
```
[tag[introduction]] -[tag[demo]]
```
! Working with Filter Results
Usually, each run of filter operations takes as its source the entire store of available tiddlers. Prefixing a run with `+` causes the accumulated results to be used as the source instead.
For example, this filter selects tiddlers tagged "introduction" or "demo" and then sorts the resulting list by the "title" field: