The simplest case is where you already know exactly which tiddlers you want. Type each title in double square brackets, with a space between each one and the next:
[[Recipe book]] [[ScrambledEggs]] [[Mom's apple pie]]
You can omit the square brackets when a title doesn't contain any spaces:
[[Recipe book]] ScrambledEggs [[Mom's apple pie]]
The double square brackets are actually a shorthand for this:
[title[ScrambledEggs]]
... which gives us the general model for any filter:
[operator[parameter]]
For instance, here's how to select all the tiddlers that have been tagged Recipe:
[tag[Recipe]]
We can reverse the meaning by adding an exclamation mark ! just before the operator. For example, we can select any tiddlers that do not have the Recipe tag:
[!tag[Recipe]]
Tiddlers can be filtered by other fields than just title and tags:
[field:serving[4]]
That example will select any tiddlers that have 4 in their serving field.
As the word "serving" isn't a standard filter operator (and isn't likely to become one), you can safely omit the field: prefix:
[serving[4]]
The filters we've looked at so far have involved just one step each. But you can run several steps together like this:
[tag[Vegetarian]!tag[soup]serving[4]]
Notice how the entire run is contained in a single pair of square brackets.
A tiddler has to match all of the steps in a run. So the example above retrieves vegetarian recipes (other than soups) for 4 people.
A sequence of separate runs will select the tiddlers that match any of the runs. We can use this to find recipes that serve either 3, 4 or 5 people:
[serving[3]] [serving[4]] [serving[5]]
If we want to ignore vegetarian recipes that serve 4, we can say this:
[serving[3]] [serving[4]!tag[Vegetarian]] [serving[5]]
By default, each run considers every tiddler in the wiki. But we can use a + sign to force a run to consider only the tiddlers that were selected by the preceding runs:
[serving[3]] [serving[4]] [serving[5]] +[tag[Vegetarian]] +[sort[title]]
This selects recipes for 3, 4 or 5 people, then filters those to keep only the vegetarian ones, and finally sorts any that are left into alphabetical order of title.
In a similar way, we can use a - sign to remove a run's tiddlers from the result so far. Here we select all vegetarian recipes apart from two:
[tag[Vegetarian]] -[title[ScrambledEggs]] -BeansOnToast
The parameter of each step we've seen so far has been in square brackets, meaning that TiddlyWiki treats it literally. But two other kinds of bracket are possible:
Curly brackets {} mean that the parameter is a TextReference, and that its value is to be looked up in a specified tiddler. For example, if we have a tiddler called Preference whose text happens to be the word Vegetarian, we can say
[tag{Preference}]
as an alternative to [tag[Vegetarian]]. This allows the preference to change over time.
Angle brackets <> mean that the parameter is the name of a variable whose value is to be used instead. Here we use the built-in currentTiddler variable in a filter that selects any tiddlers whose text contains the title of the current one:
[search<currentTiddler>]
Note that these special brackets cannot be nested. It is not possible for example to write [search{<currentTiddler>}].