created: 20140410103123179
modified: 20150124202225000
tags: [[Filter Operators]] [[Common Operators]] [[Negatable Operators]]
title: is Operator
type: text/vnd.tiddlywiki
caption: is
purpose: filter the input by fundamental category

<$macrocall $name=".operator-def"
input="a [[selection of titles|Title Selection]]"
parameter="a category -- see below"
paramName="c"
output="those input tiddlers that belong to category <<.place c>>"
negationOutput="those input tiddlers that do <<.em not>> belong to category <<.place c>>"
/>

The parameter <<.place c>> is one of the following fundamental categories:

|!Category |!Matches any tiddler that... |
|^`current` |is the [[current tiddler|CurrentTiddler]] |
|^`image` |has an image ContentType |
|^`missing` |does not exist (other than possibly as a non-shadow tiddler), regardless of whether there are any links 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, the output is an error message.

`!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">>