created: 20140410103123179
modified: 20161127142329969
tags: [[Filter Operators]] [[Common Operators]] [[Negatable Operators]]
title: is Operator
type: text/vnd.tiddlywiki
caption: is
op-purpose: filter the input by fundamental category
op-input: a [[selection of titles|Title Selection]]
op-parameter: a category
op-parameter-name: C
op-output: those input tiddlers that belong to category <<.place C>>
op-neg-output: those input tiddlers that do <<.em not>> belong to category <<.place C>>

The parameter <<.place C>> specifies zero or more fundamental categories using the following syntax:

<$railroad text="""
[{: ("current" | "missing" |: "orphan" | "shadow" | "system" | "tag" | "tiddler" | "image") +"+" }]
"""/>

|!Category |!Matches any tiddler that... |
|^`current` |is the [[current tiddler|Current Tiddler]] |
|^`image` |has an image ContentType |
|^`missing` |does not exist (other than possibly as a shadow tiddler), regardless of whether there are any links to it |
|^`orphan` |has no [[hard links|Hard and Soft Links]] to it |
|^`shadow` |is a [[shadow tiddler|ShadowTiddlers]], regardless of whether it has been overridden with a non-shadow tiddler |
|^`system` |is a [[system tiddler|SystemTiddlers]], i.e. its title starts with `$:/` |
|^`tag` |is in use as a tag |
|^`tiddler` |exists as a non-shadow tiddler |

If <<.place C>> is anything else an error message is returned. <<.from-version "5.1.14">> if <<.place C>> is blank, the output is passed through unchanged (in earlier versions an error message was returned).

`!is[tiddler]` is a synonym for `is[missing]`, and vice versa.

When <<.op is[missing]>> is the first operator in a [[run|Filter Run]], its output is always empty. And when <<.op is[shadow]>> comes first, it outputs only those shadow tiddlers that have been overridden. This is because the [[initial input to a run|Filter Expression]] contains only <<.em non>>-shadow tiddlers.

The <<.olink all>> operator is similar, but its scope is the whole wiki.

<<.operator-examples "is">>