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is Operator

16th September 2019 at 3:14pm
Common Operators Filter Operators Negatable Operators
purposefilter the input by fundamental category
inputa selection of titles
parameterC = a category
outputthose input tiddlers that belong to category C
! outputthose input tiddlers that do not belong to category C

The parameter C is one of the following fundamental categories:

CategoryMatches any tiddler title that...
currentis the current tiddler
imagehas an image ContentType
binaryhas a binary ContentType
missingdoes not exist (other than possibly as a shadow tiddler), regardless of whether there are any links to it
orphanhas no hard links to it
shadowis a shadow tiddler, regardless of whether it has been overridden with a non-shadow tiddler
systemis a system tiddler, i.e. its title starts with $:/
tagis in use as a tag
tiddlerexists as a non-shadow tiddler
variable New in: 5.1.20 exists as a variable (whether or not that variable has a non-blank value)
blank New in: 5.1.20 is blank (i.e. is a zero length string)

If C is anything else an error message is returned. New in: 5.1.14 if 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 is[missing] is the first operator in a run, its output is always empty. And when is[shadow] comes first, it outputs only those shadow tiddlers that have been overridden. This is because the initial input to a run contains only non-shadow tiddlers.

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

Examples